There is a wonderful group of people who are based at the port as "trouble shooters." I've forgotten their exact title, but their job is to handle anything that happens to people before they get to the ship that wasn't supposed to happen. They will facilitate getting you to the ship however they can make it happen, get lost luggage to you, etc.
Yes, the ship will be held for a short time IF you booked thru Disney. I know that they have held it when people were at the airport and on the way to the port (about an hour.) However, if (for example), you were snowed in at O'Hare and had not even left the ground yet, they are not going to hold the ship! They will offer you what they can....catching up with the ship at the next port or re-scheduling the cruise. If you bought the
travel insurance, there will be no fee, of course. If you didn't buy insurance, I'm not sure how it would be handled.
If you didn't buy your air as part of the cruise package (you bought it separately because you could get it cheaper), then it is your responsibility to be at the port on time. Again, if you bought a private insurance package, it would cover re-scheduling. If you bought insurance thru Disney, it would not cover the fact that your air didn't get you there. Once again, the trouble shooter crew would do what they could
IF you arrive at MCO as scheduled, there will be no problem at all. You'll be there in plenty of time.