Everlong is the only song I've really ever liked enough to learn it. I look at it as if Sabbath's hit song Paranoid was the only decent song they had that propelled their career (which is furthest from the case, almost exactly opposite). So no, to the question about in 40 years I highly doubt it. We would never know his name if he didn't have the Nirvana gig.
You could say that about a lot of musicians I imagine but a few of them had equal to better music on their own. Nothing Grohl did ever surpassed Nirvana imo and I'm not a huge fan of them either. Compared to today's standard they'd be a breath of fresh air. I didn't mind them help kill off hair metal. No bitterness there.