What happens if you get mildly sick, I guess you can hide it for a few days and then carry on with the cruise.
But what will happen if you are noticed being sick, do you get kicked off the cruise and lose out on the rest of the trip and $$
The COVID testing and protocols vary by itinerary and cruise line, but I've never heard or seen anyone getting kicked off. It seems they have different isolation protocols. I've experienced two protocols, unfortunately.
While visiting EU ports, I was told that because I tested positive, I had to move to a special section of the ship for the remainder of the cruise (2 days). I was on the same ship for the next itinerary, but the protocol was different: stay in your own room for 5 days after you test positive, and mask once you get out of isolation.
Considering not reporting your symptoms, and doing your own isolation, that actually came back to bite me, but it's a weird situation. The morning of the cruise, I tested negative, but they didn't ask to see the documentation at boarding. I had uploaded my proof of fully vaccinated status, though. The next morning, I had a scratchy throat, but it went away, and I was hoping it was nothing. But when the fever came, I knew it was something, and kept to my cabin except for masked trips to the buffet and eating outside. Then, on day 5 or 6, because I was on the ship already, the cruise line said they would do the pre-cruise testing for the follow-on cruise (I was doing back-to-back). By the time they tested me, it had been 5 days since I had symptoms, I felt much improved, no fever, but I still tested positive. So another 5 days in isolation! The last two days of the first cruise I was moved to the COVID hallway (EU regulation) which was identical room to my original room, including a window. When the follow-on cruise started, I was moved to my balcony room, but still compelled to stay in the room and get room service food.
Oh, and the cruise line gave me 5 days credit on a future cruise. I think they know if they don't address this problem in a way people can manage, demand will drop off hard. Based on the comments in this thread, it sounds like going on a cruise in the fall of 2022 meant it's quite likely you're gonna get it.