Did his writing fall off? Is there something in his later work that was really bad? If not, I don't see any reason to think he couldn't do it again, and he's probably got more ideas on how to do it than anyone.

Twenty years ago he was the only one who could do it. He wrote the manual on genre-bridging action/comedy storytelling with an ensemble cast. It's why Avengers worked when it probably shouldn't have, and any similar successful properties since then have followed his lead.

I'm not trying to deify the guy, but I think the unique nature of his talent is swept under the rug since he got canceled.

The fact that people change a lot is a big problem for me with Firefly to begin with, because I loved Firefly, but...I was like 17 when I watched it. I'm in my late 30s now. I do not feel the same about it anymore already, in ways where I don't think it should come back at all.