Misty Escape: When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it isn't in sunlight or running water. If it can't transform, it is destroyed.
While it has 0 hit points in mist form, it can't revert to its vampire form, and it must reach its resting place within 2 hours or be destroyed. Once in its resting place, it reverts to its vampire form. It is then paralyzed until it regains at least 1 hit point. After spending 1 hour in its resting place with 0 hit points, it regains 1 hit point.
The moonbeam description says:
A shapechanger makes its saving throw with disadvantage. If it fails, it also instantly reverts to its original form and can't assume a different form until it leaves the spell's light.
The moonbeam forces the vampire to revert to its original form, but the Misty Escape trait also states it can't revert to its vampire form.
What will happen then? Does the vampire got destroyed? Does the vampire revert to its vampire form with 0 hit points? Does moonbeam fail to forcibly revert the vampire?