The spell plane shift can be employed to escape a node
Part 4: Nodes of Elemental Evil on Transportation says, "Escape from the nodes by other means is highly unlikely. A wish, plane shift, and certain other spell effects may allow transportation, as detailed in the following list of spell modifications" (Temple of Elemental Evil (1987) 107). Later, on Modifications to Magic on Spell Variations among Cleric Spells has this entry: "plane shift: Allows escape to the plane of the spell component's orientation" (109).
In other words, the spell functions normally, but the DM is expected to enforce the plane shift spell's focus component, the acquisition of which, this adnd and adnd-2e player can tell you, was usually far more onerous than it is in the typical campaign of dnd-3.5e, but good on the PCs if they've already the forked metal rod.
So, if in possession of the focus, the PCs are good to go… and arrive 5d% miles from their destination on the new plane then 5d% miles from their destination on the Material Plane. (Being off-target in such a fashion isn't part of the adnd spell plane shift, but the adnd spell plane shift didn't allow specifying a destination either, the affected creatures apparently appearing on the new plane at a DM-determined destination, and its subtext making the older version of the plane shift spell a last resort.)
You're probably already aware that the spells teleport et al. don't work in a node, but, just in case, another note on Magic-user Spells says, "teleport: Cannot be used to escape from the node" (ibid.). Further, the "entire wall separating the northern and southern portions [of Dungeon Level Three]… defies any attempts to pass through it… by way of teleport or dimension door [or] plane travel…" (75).