This is absurd guys. We have one guy's story, from his perspective. For all we know, the OP sat around and did nothing productive. The founders had a reason to terminate him - be it what others would call a "good reason" or otherwise. Perhaps there were issues the OP is completely unaware of?
What will happen? Will YC yank funding over this? I hope not -- that would set a dangerous precedent and make me, for one, that much less willing to pursue YC funding.
If the founders didn't want the OP before -- they especially aren't going to want him now that all this has occurred and threats about getting YC involved etc.
The bottom line -- you can be terminated for any reason, even if it's the color of your shirt on that particular day. Does that make it "right"? Well, that's a perspective thing.