Happy STS! What is one thing your character regrets? If they could, would they go back in time and change it?
Happy STS! I'm so sorry this answer is late!
That depends on the character, again. Different people regret different things.
Tip? Tip's biggest regret is and remains not being able to save Pyrhha and Gretchen. Yes, he very much... dealt with... the hunter that got her killed, but he hated losing a student. Any student, they were at Beacon to learn. Of course he'd go back and change it, their lives mattered too.
Glass' is more... complicated. Gretchen still happened, she's still a regret, but not his biggest one. Honestly? Glass regrets not having committed patricide, not having claimed his siblings as under his protection. He could have done that. It would have been messy, but he could have. Whether he'd go back? No, I don't think he would. But he'd be tempted.
As for Wesley? Well, at this stage he still believes that he went mad, that the Wizard isn't real. He just... outright regrets leaving. Regrets leaving his friends, his twin, his family. Leaving Qrow. He's so scared that that isn't fixable, and he might be right. He'd go back in a heartbeat.