Capaldi's great, and if it were based just on his talents alone and their were no other factors, I'd absolutely say he should stay as long as possible
BUT
No-one but the fan's know anything about this or that showrunner. If the show is bad to them, they associate it with the current doctor. If there is a new doctor at the start of Chibnalls shiny new era, then new viewers, or previous viewers who hated Moffat's Capaldi series's and stopped watching will take a look once more to see if they think this new doctor's era is for them. If it's still Capaldi in the role, then most viewers won't know anything has changed and will continue to not give it a new chance.
What I'm trying to say is, the show is and always has been bigger than one actor, and despite Capaldi being a great actor, I think that he should go with Moffat to allow Chibnall, and the show to have a chance at mainstream popularity once again like it had with RTD. That is why I have voted that he should leave with Moffat.
I think if you could actually somehow prove that a new era would be better served with a new face, then as a fan, Capaldi would probably voluntarily go when moffat does.