I keep trying to get my players' characters to sacrifice themselves, but they always manage to destroy the Mirror of Opposition and "themselves" before I can pull it off!
Very cool story. With the availability of raise dead, ressurrection, wish, etc. in D&D it is generally pretty hard for PC's to truly not be able to come back. The OP's situation was truly one where there is no coming back, which really makes it all the more significant.
Evander Con Rhys, one of my old wizard PCs sacrificed himself by dropping a Mordenkainen's disjunction a much more powerful tyrannical wizard and reducing a man who sought to breed the perfect race of humans to a frightened man in his underwear. All the Emperor who controlled an army numbering in the hundreds of thousands could do was to cast the wizard into oblivion. My character got to give a one fingered salute as he faded away, watching his erstwhile allies stop fighting the summoned creatures and go after the real threat. I left the DM flat footed as he had not prepared for my spur of the moment action -- which was in keeping with the character's stubborn habit of getting things done no matter how hard of a task.
The character earned the respect of the other PCs, who were previously indifferent to a non-noble in the group.