Yes, UST can collapse but i doubt that it would bring everything down. It would just affect some coins. USDT has been suspected not to hold as well but as they have insanely well backed up it with real world value, it won't crash.
Although there is a little suspicion on USDT, but until now there are still very many people who use USDT
because the stablecoin is still very good and almost everyone still believes in USDT than UST you mean it.