There's no such thing as a wish that irrevocably transforms a character. The best it can do is duplicate another spell, like polymorph any object or some such. No polymorph effects are instantaneous-- they all have an ongoing duration-- which means they're subject to dispel.
So, you can get your dwarf back with a simple greater dispel magic. If your DM declares that won't work, have your mage bust out a disjunction; that sucker can even destroy artifacts, so it will effortlessly take apart that simple little wish. And it won't cost you 5000 XP.
If your DM tries to argue that the transformation is truly irrevocable and permanent and cannot be undone in any manner, inform him that he's a tool, and find yourself a new DM.
So, you can get your dwarf back with a simple greater dispel magic. If your DM declares that won't work, have your mage bust out a disjunction; that sucker can even destroy artifacts, so it will effortlessly take apart that simple little wish. And it won't cost you 5000 XP.
If your DM tries to argue that the transformation is truly irrevocable and permanent and cannot be undone in any manner, inform him that he's a tool, and find yourself a new DM.