Technically, they could have. But it wouldn’t have really been Nirvana without Cobain. It was pretty much Cobain’s cult of personality. If they had tried to continue without him, it would have been another one of those bands that starkly contrasts between before and after and the comment above would have been about never knowing Nirvana in its heyday.

Even if the continuation was good (and Dave Grohl is proof that there was enough talent for it in the rest of the band), it would have still been tainted by the lack of Cobain.