Well, Nirvana was had a heavy fan base before he died. I don't think people like them just because he died young. Did more people notice Nirvana, afterwards.. probably. But that doesn't say they weren't noticed at all, before the fact. Nirvana definately had an impact on the 90s. Whether or not they're still as remembered as much now or not.. and even with taking into consideration where they pulled their own influences from. Nirvana's legendary.

Sometimes musicians die young, because of problems from this world, but doesn't make them less talented or hand them undue credit.

Growing up in different generations contributes to a person's viewpoint on this matter.