You keep editing your message lol. I don't have all the answers, but the whitepaper suggests that any exploit will be contained in the sidechain. The parent chain will be unaffected
sure - besides the bloat of course.
All this doesn't rule out the possibillity for sidechains to collapse in on itself in case the two-way-peg is open to exploits which it likely will be.
How does a blockchain collapse in on itself exactly? Is it like a polar vortex?
no, the two way peg fails, all the locked bitcoin get stolen - the sidechain stops to exist with no prior warning at the flip of a switch.
People having value parked on the sidechain will be left with nothing then...
If the sidechain is of no interest to you then you stay on the parent chain. No big woop I should think. But for the rest of us it opens up some interesting possibilites