I would see the masks to be set out like clean towels everyday. You can not wear the same one for a 7 day cruise. The first one given to you as soon as you show at the port.
If the mask is "Anti-virus" then it would have to be like a N95 mask. I could see the cruise lines them selling them on a web page for general public to buy and wear since it looks like masc's will be around for a while.
You will have to remove it when you get on the ship after port days for security to check your picture that you are you. I could see them holding people back 6 feet as you get checked back on and a Plexiglas divider between guest and security for check in.