First of all, that is brutal, very sorry to hear that.
Here's the good news, though: Disney is about more than just riding the rides, and seeing the shows, it's about getting together as a family and taking it all on. I'm not as grizzled a veteran as some people on here, but I've been a few times, it's been different every time, and a trip with one group of people is entirely different than a trip with another group of people.
On our most recent trip, we had a few days where it was my wife and I with her extended family, a few days where it was just the two of us, and a few days where it was us plus my parents and our daughter. It was like having three different vacations in one, as each leg had its own unique feel to it, and we enjoyed each for different reasons.
I say go. Sounds like you've had a lot of fun building up to the trip, and the anticipation and the bonding you had while planning is something your ex can't match. Let your kids have the pay off of getting to experience the trip that you all planned together.
Regardless of when you go, have fun!