Time Lords are limited to 13 regenerations. Not sure if its a law or a physical limit. The Master originally reached his Regeneration limit and was in a charred, decayed state for several of his appearances before he restored himself. THen the Time Lords offered him a new cycle of regenerations for helping them with something. Can't remember if he got those or not...Youkai said:Hmm well there were better episodes even thaught it was partially very interesting to get to know more background on river.
still "she used up all her remaining regenerations" ... wtf? didn't watched all old episodes yet (just to much) but i allways thaught the regenerations were more or less "endless" ?
They never needed her to lose her regenerations either... Her death in the Library was from doing something that would have killed the Doctor outright as well from what I remember. The sacrifice of the immortality for a man she barely knows, and was supposed to kill is the main point of the scene.