Here, the accommodation, for, say, a store, is that someone will shop for you. It isn’t that people can go into mask mandatory spaces unmasked. Seems to me that the accommodations the court offered were reasonable. Under the ADA, you don’t have to get your preferred accommodation.
As far as the options offered and not giving a continuance, generally, older cases are harder to get continuances on, and, critically here, you will almost never get one at the stage where you’re choosing a jury. Basically, trial has started. You don’t get months’ delay at that stage. You might get a day, for something unexpected, if it’s dire. You don’t get to the eve of trial and then bring up an issue that you knew about all along, refuse reasonable accommodations, and refuse to comply with known court rules until you get the delay. No trial court is going to go along with that.
And yes, without prejudice means the plaintiff can refile. Then they can presumably skip ahead in the process, because things like discovery should be over as they were ready for trial before. So, it clears the case from the court’s docket until they refile, and probably puts them at the back of the line again for a trial.