They will acquire a significant portion then fractionally reserve it. They are the same beast as FTX, just more organised. They won't go bust in one cycle, they will manage draw downs through regulation and influencing monetary policy. When they do get exposed they will ensure that so manny people would get rekt, that the government will intervene like they did with gold. 

An ETF is the final fiat boss for Bitcoin to defeat to destroy the central bank.