I wish I knew. Ciro Nieli had this great idea in a spotlight video you can see on Youtube that would've had him breaking away from the Foot Clan at some point and trying to find his own way in life. It's a great idea because it would've given depth to a character who had an uneasy alliance with Shredder (like Karai) going into S4 despite his loyalty but they blew that from "Earth's Last Stand" onward. And that's also disappointing when you consider that Tiger Claw not only got worse as a character from that point on but it was a missed opportunity due to the fact that this franchise doesn't have a very good Rogue's Gallery.
Basically, when "End Times" came along, Tiger Claw should've either sacrificed himself in the midst of battle so that the heroes could win or he should've been killed (preferrably by Karai) afterwards.
He's not the only one who didn't return, though others are allies, so its expected they might return. He on the other hand, could've left, maybe he's with Alopex, a team up like before, or he's left New York. Its like the questions about Pigeon Pete in the Mutanimals, Y'gythba, absent from the rest of the season and we probably know why, if what was posted is true about what the writers said about her. that fight the 1987 turtles had with Tiger Claw. Was it explained how it went? I know they lived, but I wondered if they were hurt badly, like the 2003 turtles, when they went to the farm house to recover. Hence why it took a while to see them again.