It's not out of the realm of possibility, you are right. I just think it's going to take something drastic for Garber to cancel or postpone this thing. FC Dallas and possibly Nashville dropping out isn't that, in my opinion.
The USA and, more specifically, Florida are not Germany. Germany has leaders that believe in science and that has helped the Bundesliga get up and running fairly safely. Florida isn't so lucky, so a massive outbreak isn't out of the realm of possibility.
It's one thing to say in March the regular season will be put on hold as everyone else is canceling stuff. But four months later, to plan this tourney and then bring all the clubs down to Florida in the past week or so despite the increase in cases and continue to push forward is an indication to me that Garber wants this to happen badly and isn't going to be easily persuaded in the other direction. I don't think the clubs would be in Orlando right now if there is any chance this is gonna get postponed.
Regardless, all we can hope for is a fun event to watch and full safety for the players, staff and hotel workers.