This follows the pattern we saw last year. Most spots were gone after rounds 1 and 2, but some spots were left (and some people obtained offers) all the way to the 5th round.
This is a complicated question. Sure, you can always violate your match commitment and just plan to never match again. But your PROGRAM could be considered a match violator for keeping you, and they could be excluded from the match. I'm sure they like you, but probably not enough for that. You can always apply for a match waiver and see what happens -- but that will take some time, and your current program may be unwilling to hold your spot for that long.
Being a "previous grad" isn't a huge red flag. Lots of previous grads are in that category because their applications have problems and they failed to match in their first year, so it's no surprise they will have trouble in their 2nd match attempt. But if you are an AMG without huge problems, and take a gap year and do something useful with it, most programs will happily consider you for a spot.
I expect your suggestion of a class action was hyperbole, but you have no right to a job, I don't see what you plan to sue over. You can keep looking for a position, hope a program opens a new position, or that someone can't start due to a problem, etc. or you could try to challenge an H visa -- I have no idea if that's realistic or not.
If you want to go into Peds, you'll need to start as a PGY-1. You will get minimal credit for your TY. Even if you wanted to go into IM or FM, you'll probably need to start as a PGY-1 (you might get 6 months of credit). credit is completely up to your new program -- they could decide to give you none.