A friend of ours just lost their Australian Cattledog at 15 years old, she also had a cleft palate. I don't think she had as many surgeries as your girl but she did have a special mouth piece made for her so food and water could not go through the hole.
The specialist made her a plate, but she rejected it and it had to be removed the next day. The thing that did her the most good was removing 4 of her upper molars, and using the gum tissue to close part of the cleft. She had to swallow most of her food whole anyways, so the loss fo the molars didn't impact her much. She could still inflict plenty of damage with the rest of her teeth though.
Are you going to get him another playmate? I sure hope he feels better soon.
I've thougth long an hard about it, but am leaning towards not getting another dog at the moment. Alex is a pretty tired old guy, and I'm afraid anything other than another very senior Basenji might just be too much for him. Up until a year or so ago, he was VERY alpha and I'd be afraid he might want to fight another dog. Cassi was very very submissive, yet he still whipped up on her every once in awhile. I've been trying to console him by letting him stay inside when we're home. Most of the time now he just paces for an hour or so, then sleeps.