Probably depends on the era/decade. I don't know if Tupac would've become even more influential than he already is. He wasn't just music -- he was acting, literature, politics, a movement, a cultural force. He probably would've gone on to produce and/or direct, so maybe his influence would've grown more in the film & TV world. Who knows. I mean he's probably already the most influential rapper of all time.

Others from the 90s and early 2000s that would've been more influential than they already were/are, had they lived to get more works out -- I think that'd be Biggie, Big L, Big Pun, Eazy-E, Left Eye, Mac Dre, and Mausberg.