i have thought about this a lot personally. lets just say he didn't kill himself. i think pat smear would have come on for the fourth album. i think their fourth album would have been their most solid , as nirvana was always meant to be a four piece, plus the demos towards the later years definitely leaned more alt rock style, think REM. i think it probably would have been over in some form maybe one album after that. Dave reportedly hated Kurt and for what its worth i think Kurt was a total dickhead in the first place. if krist continued to pursue music im sure he would have stayed with kurt. and who smear would have sided with is completely up in the air. through the 2000 "nirvana" and "foo fighters" would have been moderately competitive towards each other but with their best days firmly behind them just like foo fighters is today. maybe in the late 10's or early 20's they would do a reunion show possibly leading to a new, underwhelming album, purely for the money as whatever beef they had would have been squashed by time. as for kurts personality, see Eddie vedder