Talk How colossally dumb Dorukan was [Untagged SoD spoilers]

[Yendor]

This also assumes that Dorukan did not find ways to protect his tower/dungeon against teleportation, which would be one of the first things you'd want to do if you're trying to ward a place against high level casters (right after protecting it from scrying effects). In which case it may very well be reasonable that Dorukan didn't prepare multiple castings of teleport if his dungeons' own defenses mean teleporting is a one-way trip no matter what.

And in fact, Dorukan did protect his tower from teleportation.

Anyway. The result of the fight is a foregone conclusion; the exact details are irrelevant and it adds nothing to have Xykon's speech interrupted by Dorukan casting ever more feeble spells. What Dorukan does is not the point of the scene.