how seized by FBI and they came back and they refund?
that's impossible!
Because it wasn't actually the servers that were taken, but rather just the domain, which is usually registered somewhere where the US have some sort of jurisdiction.
It's a setback for sure, but nothing compared to the FBI actually taking their servers and thus their funds.
I'm wondering if there are any domains that are so to speak "unseizable". Apart from .onion ones, i don't think there are?
That's hard to say and to be fair I can't understand well. For example thepiratebay changed their domains but finally returned back to original one, how did this happen? Everyone knows it's pirate, just seize every domain they own, why don't they do that? Another example is rutor.org <-- this domain was seized but they move on new-rugor.org <-- why isn't it seized? Domain is still .org