As posted above: hire a new guitar player to make the band viable. Always invite the stroke victim to jams. I hate to say it, but keep the sound man in the loop to keep his guitar wayyyyyy down in the mix. If you play a song he can still do fairly well on a lead break, sure, let him fly his kite. But leave the journeyman chores to the guitar player you hire, telling him up front the situation in the audition.
Syd Barrett comes to mind after he fried his brain on acid. The difference is that nobody can predict a stroke. I had a similar situation in the early 2000's, when I had a mini-clot-stroke that got my left hand. All of a sudden, in the middle of a gig, my left hand just quit working. I wasn't about to let it stop me, and I made up my own PT regimen, starting with thumb to finger touches, and working myself back up to full playing ability. Nothing was going to keep me down, even if I had to raise the music stand playing guitar in church band so no one could see me and I could as necessary use my right hand to adjust my left hand on the frets on the fly. I am blessed and thankful that now, comparing my playing to recordings before the mini stroke, you can't tell it ever happened. Ironically, my right hand took up the slack (I am left-handed, but always playing conventional right-handed instruments) and where before I could hardly fingerpick on guitar, now I have some modicum of fingerpicking ability with my right hand I never had before.
By contrast, my band from the '90's lived through a similar situation a few years ago. Our lead guitar player was great. Yes, great. We have the studio tapes to prove it. But, after we disbanded, with family, a job transfer, and life generally, over the course of twenty years he has completely lost his chops. Completely. When he does come to visit, I usually have to fix the same niggles on his guitar that keep cropping up as did then, and then all he can do is play some of the chords. He can't even play his own leads that he recorded 25+ years ago. He finally figured it out a couple of years ago when, well, let's just say he turned red in the face so we all stopped, took a break and popped open a beer. Now just shares a beer with us when he is in town when we jam. It's actually rather tragic. The upside is that his career and family are doing really, really well. He just can't play anymore.