It really depends. If all of your itinerary is together, the airline will reprotect you. This will only happen if you book your air through the same place you book your cruise.
If you miss your flight and you've purchased it seperatly, theres nothing the airline has to do. Though they probably will put you on another flight, but that could be HOURS away..
I wouldnt try to save a few bucks and risk missing a plane on seperate domestic tickets, which is what you have.
Brandy