I don't know he economics in your games, but in mine, a commoner makes around 30-50 gp a month, and a noble around 150 gp a month. So, if a NPC rewarded someone to save his life, I think that 30,000 gp is way over the top of believability. I wouldn't mind my PC find such a fortune in a forgotten treasure, but someone giving it to them just to say "thank you"?? However... lets say that the wizard is not of a good alignment, and that he prefers to get rid of the gems for a very good reason. Now, it's the PCs who will have to deal with the problem.