When I had Covid this past December, my doctor immediately prescribed Paxlovid. My severe flu-like symptoms went away completely within 48 hours. I continued to isolate as recommended. The risk factors for Covid co-morbidity are not all immediately-life-threatening-you-should-never-cruise-again conditions. Asthma, age over 50, BMI over 30, etc .... MAAAAANNNNY cruisers fall into one or more of these categories.
Before my next cruise (a 9-day in August), I'm going to see if my doc will prescribe me Paxlovid to take along, just in case. If I test positive at any point, I'll be able to take care of myself. And, if my isolation period ends while I'm still onboard, I know I'll feel well enough to enjoy what's left of my vacation.