It is unlikely.

The 3.5 Ravenloft Player's Handbook, published in 2003 by Arthaus under license from Wizards of the Coast, gives insight into the setting in a D&D 3.5 context. According to page 9 of that book, "Travel":

The Mists even restrict planar travel, unless the Mists allow it, no force short of a major artifact or the direct intervention of a deity can provide passage to other planes.

Epic-level magic is potentially in the ballpark of the required power level, but casting one from within Ravenloft is another matter entirely. According to page 30, each domain has a magic rating which limits the maximum level of spells which can be cast. Only the most extreme high-magic realms, rating 6, allow epic level spells to even be cast. Rating 5 domains only allow up to 9th level magic, which is insufficient: the book notes in particular that even the 9th level spells gate, miracle and wish fail if used in an attempt to escape.

However, the magic rating system is optional, and even then it doesn't apply to spellcasters outside of Ravenloft attempting to rescue people from the plane. On the other hand, the Epic Level Handbook notes that epic magic items are not quite major artifacts (they are on par with minor artifacts), and one may reasonably say that epic spells are not quite divine salient abilities (as defined in Deities and Demigods).

A DM could of course allow the creation of an epic spell specifically designed to escape the plane, but of course this would be a matter of DM's discretion. A possible precedent is the AD&D 2e module Die Vecna Die, where he uses the Language Primeval, something defined in the Epic Level Handbook p.71 as part of epic spells. However, in that case he merely used epic magic to siphon divine energy from another deity to attain godhood, after which his escape was simply performed by divine intervention.

The topic of escaping Ravenloft in D&D 3.5 also is discussed in two previous questions, Is there a way to leave Ravenloft? and How can I escape Ravenloft in spite of the dark powers?.

Vecna canonically did it once, but only by ascending to godhood.

The Ravenloft setting received little first-party support during the D&D 3e era when epic spells were part of the rules, being mostly relegated to third-party sourcebooks and the occasional Dragon Magazine article. Epic content also received little support, and while the Demiplane of Dread's continued existence was confirmed in Dragon Magazine #351, the question of how epic spells interact with the Demiplane was never answered.

The existence of reliable methods of escaping the Demiplane of Dread has always been vaguely defined, as a feature of the setting's tone. If you're powerful enough to come and go as you please, it kind of defeats Ravenloft's intended purpose. According to Dragon #359, we don't who the Dark Powers are, or exactly how powerful they are, or exactly how Lord Soth escaped, and so on.

Domains of Dread and other AD&D 2e sourcebooks make it clear that even 9th level magic like wish does not allow escape, although it is possible by other uniquely powerful means including the artifact Rift Spanner and the planar World Serpent Inn (Dragon #351).

Regarding epic spells in particular, the Epic Level Handbook p.71 usefully informs us that they are effectively synonymous with several forms of magic from the AD&D 2e era:

In various times and places, epic spells have been personified as "The Serpent," codified as True Dweomers, and encoded as part of an ancient lore called the Language Primeval.

These do in fact overlap with several products with Ravenloft support:

• In College of Wizardry, which is optionally located in Ravenloft, the archmage Japheth Arcane researches the Language Primeval to find a way to escape the plane. It is unclear whether he can succeed.
• In Vecna Reborn, he uses the Serpent to bypass the impenetrable barriers between domains. However, according to Dragon #359 again, it is unclear if the Serpent is a deity-like figure or just an illusion of Vecna's madness.
• In Die Vecna Die, Vecna inscribed tablets with a true dweomer in the Language Primeval, the latter asserted to be the language of the Serpent. His spell allows him to absorb the essence of another demigod, become a full deity, and escape the Demiplane of Dread. However, it may be that becoming a deity is what allows him to escape, and when the Lady of Pain re-orders the cosmos to prevent similar attempts, it could be that she closed this loophole.

In other words, escape from a Ravenloft domain using epic spells is possible, and we know because Vecna did it once. Bypassing the barriers between domains with epic magic is definitively possible (Vecna Reborn), and while it required a unique ritual, that sort of thing is par for the course with epic spells to lower the check DC. The words of Creation Once Spoken are defined in Die Vecna Die to be part of the Language Primeval.

Vecna also uses epic magic to escape the Demiplane of Dread entirely, but since the purpose of the spell was to ascend to divinity, it may be that he simply used divine power to escape. From the AD&D 2e sources it is canonically unclear whether the Dark Powers are more powerful than the gods, or the gods merely chose not to intervene.

Various artifacts were also involved in Vecna's escape: the Eye of Vecna, the standing stones at Torvag Baragu, and Vecna's inscribed tablets themselves. Die Vecna Die p.46 suggests that the Hand of Vecna and Eye of Vecna are potentially able to allow teleportation out of the Demiplane of Dread, but do not function during the adventure module because Vecna, the artifacts' master, does not will them to. At any rate, the potential of artifacts to escape is attested in the Ravenloft Campaign Setting, Realm of Terror, p.119:

Because of their unusual power and purpose, artifacts and relics may transcend the limitations of Ravenloft. At the Dungeon Master's option (of course), spells cast from an artifact or relic are unchanged by the demiplane, as are any spell-like abilities. These powerful items may even help characters escape from Ravenloft. An evil artifact may not want to leave, however.

In other words, while he did escape the Demiplane of Dread using epic spells, it is unclear whether he also used divine intervention, artifacts, loopholes which no longer exist, or merely had the consent of the Dark Powers. Possession of an artifact could also be a necessary mitigating factor to the spell DC, and the upper bounds on Seed: Dispel suggest that it can can dispel supernatural abilities and affect even artifacts or the spells of gods, which might even include the abilities of the Dark Powers.

Including third-party sources

If we expand our sources to the officially licensed third-party books, page 9 of the 3.5 Ravenloft Player's Handbook published in 2003 by Arthaus asserts:

The Mists even restrict planar travel, unless the Mists allow it, no force short of a major artifact or the direct intervention of a deity can provide passage to other planes.

Escape by artifact or divine intervention are both attested in AD&D 2e works, but this book asserts that this is the minimum power level, which may exclude epic spells. Epic Level Handbook suggests that epic magic items are on par with minor artifacts, not major artifacts, and even so "artifact" denotes some quality beyond epic magic items. High Level Campaigns p.135 also makes it clear that similarly, True Dweomers are also less powerful than divine salient abilities:

As powerful as a true dweomer is, it is still mortal magic. Quest spell effects, representing a deity's direct intervention in the world, generally cannot be countered by true dweomers.

Ravenloft Player's Handbook p.30 also asserts that magic above 9th level, specifically including epic magic, can only be cast in exceptionally high-magic domains, although this does not preclude the possibility of rescue by someone from outside, which is technically what Vecna did by tricking Iuz into casting the spell for him.