I wouldnt save Fireworks for the last day you never know if they will be canceled etc. I got teary eyed when Mickey finally took Murray down & Fantasmic! went down knowing it wasnt going to be part of our trip was a HUGE deciding factor(well that and peter pan also being down)in pushing our trip into a holiday one. With all that said it might still be down so I am not holding my breath.
I have never seen WOC & am planning on doing a dessert party but I wouldnt of gotten emotional if it went down during my visit -- so that says a lot. I have heard they do it rain or shine so you have no problem with it being canceled. I would book the dessert party(or plan on just securing a spot) and then wait to hear if F! is back and running & you will have plenty of time to cancel.
Like someone mentioned you could technically try to hit up both fireworks & F! in one night if you move fast and dont try to secure early spots. If I only had 2 days I wouldnt waste time staking out a spot to either & if F! is back and running you could do one of the reserved dining to get a spot.