Honestly if someone wanted to try the Test of the Starstone in my game, I don't know if I could come up with anything in game awesome enough.
I'd probably chat with the player out of game and offer the three obvious choices:
1.) Die/never come back out and become another name in the Shrine of the Failed
2.) Come out richer and more powerful than imaginable, but alive
3.) Become a God/Goddess
I think having a good heart to heart with the prospective player would go a long way for me. I know it's not as interesting as potentially coming up with a mega-dungeon or fiendish traps and puzzles, but I don't think I could do it justice for my players and man I'd hate to let them down. Instead, I'd want them to tell me what their ideal result for their character would be and go from there. Keeping in mind of course the context that nobodies with little to their names don't really become deities. Still, I'd work with them to come up with something neat that they liked.
Either way, whatever choice they made would be the capstone to their character and the end of that character as a PC.
fs