If Tesla purposely dumps their BTC holdings, there will be a short-term crash on the market, the crash can possibly get longer if Elon uses Media to FUD the BTC market.
There can be crash, the market price of bitcoin could fall and definitely almost all other cryptocurrencies, but I am definitely certain that it will be short term, it is not going to last and the market will rise just like when Elon Musk says Tesla no longer accept bitcoin. The crash would also never be like that time, it would be milder this time, no matter how Elon Musk is try to manipulate the market.