It's very unlikely that you'd be bumped from a flight for which you're holding paid reservations. Make sure you get your boarding passes via online check-in as soon as you can inside the 24-hour prior limit. By Sunday, the airport itself should be operating pretty normally.
The real question is whether the planes will be where they're supposed to be by Sunday morning. With planes unable to fly on Wednesday, the "domino effect" is bound to happen and it's not certain that those ripples won't last into the weekend. I suspect, however, that you'll be fine.
In the future, I strongly recommend that you fly to your embarkation city the day before your cruise, just to give yourself some wiggle room in case of service disruptions, mechanical difficulties on the day of sailing, etc. If nothing else, being in a Miami hotel the night before your cruise will give you tremendous peace of mind, which is a great way to start a vacation.