Not necessarily, because it will depend on the incoming class, but your chances should be excellent. I'd say the most important thing is to make sure you are in very close contact with the Adcom. Make sure they know that you really really want to go there, that it's your number one choice, and that if it was not for circumstance you would, and update them about what is happening etc. (and yes, ask for a deferral, even if they don't do it.. they have the power to make exceptions).

I agree with what Jon says. It's not guaranteed but it's highly likely. Additionally, if it comes down to a reapplication, in addition to staying in close contact with the admissions committee, document it in your optional essay. It doesn't hurt to document it and various people can see that file so it's good to cover that base as well.