I failed the strength check despite being a paladin and using inspiration. I never saw him again even after getting through nearly all of act 2. I’ve asked this before, maybe even in this community, but no one gave a concrete answer, likely because the game was still new.
I think only Lae’zel and Shadowheart really have multiple chances.
Gale, Karlach, and Astarian only show up in a single place.
Wyll has a couple of places, depending. If you don’t recruit right away, he’ll show up at camp if you recruit Karlach.
He’ll also just stand around near the entrance of the grove on the left side of the road, just past the gate. I didn’t even know existed my first playthrough until I was through with the Underdark. Then I read about him online, went back, and found him there.