What would happen if the bitcoin ETF are rejected?
What has happened has already happened.
In July SEC rejected the ETF proposal by Winklevoss brothers.
The Securities and Exchange Commission rejected on Thursday a bid by the Winklevoss twins to create an exchange traded product for Bitcoin, citing the potential for market manipulation and a lack of liquidity.
I am not sure if you understand what ETF means but I am assuming that you are asking about if SEC decides to reject all ETF proposals in the near future. If that were to happen, I don't think the Bitcoin market will dump any harder than it already has.
The fallout of ETF decision is a large dump of Bitcoin which crushed the price to about 6100 dollars per Bitcoin. I don't think BTC will go below 5500 dollars. Since alt coins are kind of pegged to Bitcoin price, I don't expect much price movement in the alt coins in the next few days.
[Note: The answer reflects the opinions of the author. None of this is meant as financial advice. Make your own decision if you are investing in crypto.]