First off, the poor coaching led to being in that situation to begin with but...
There is no excuse for not switching all picks with 2 seconds left, doesn't matter what the result is. Lamar Hurd said it on the broadcast before the play that this situation is automatic switch on all picks. Do you disagree with him?
If Tolliver switches on Korkmaz and he hits a contested 3 then fine.
If Dame gets stuck on Horford and he posts him up or gets an easy 2 on him then fine, we still have OT.
If Horford gets Dame to switch on him and makes a contested 3 then fine.
There is also no reason to guard the inbounder in that exact situation. With 2.2 seconds left Simmons doesn't have enough time to get to the basket for a 2. He's literally never made an NBA 3 point shot so if he makes his first NBA 3 to win the game then fine you live with that but with that amount of time left there isn't really a situation where he'd get a great shot anyway.