FWIW - I believe there will still be some changes in place come next March. For example, I'd bet that hand-washing before entering the buffet, specialty dining and kids clubs will be mandatory.
But masks? I just don't see it. There might be some cruising die-hards who are happy to sail with a mask mandate right now. But the general U.S. cruising market will not accept it long-term, IMO. Especially if mask mandates for land-based vacations are no longer in place.
More likely, proof of vaccination will be required in order to sail, with masks being suggested/recommended for those with risk factors. And a waiver of liability for
DCL if you get COVID-19 while on-board. Non-negotiable, meaning if you don't like it, don't sail.