Say for example a tier one exchange gets hacked for 10.000 Bitcoin. (About $200.000.000) Exchanges immediately coordinate and bribe miners with at least 51% hashrate to pick a block just before the hack and start a new chain from there. Hacker on the meantime can also bribe miners and encourage them to continue on the original chain with the hacked funds. Is there any other plan? What contingency plans could they have on such event to annul the hack?