I think Cobain and Grohl were about to go their separate ways regardless and Grohl's career wouldn't be that different with Cobain still alive.
But I also think Cobain would have kept making music for a few more years anyways, he and Novaselic would have found a new drummer. The new music might have been pretty different from the old, too. We will never know.
Cobain probably had borderline personality disorder. There is no way to treat that chemically, and he was trying to treat it with narcotics. But if he had just gone to therapy and taken it seriously, he could still be alive today.

---