What happens to my invite if all courts are booked out?

Nothing. It remains in place. You never know, some-one might cancel and you might be the first in line to get it for a match of your own. ManageMyMatch will do this for you automatically.

You can even invite when you know all courts are booked out. Maybe you are really keen to play at that time and you want ManageMyMatch to give it to you as soon as some-one cancels.