I’m really sorry to hear about this, it’s so sad.
I work in brain injury rehabilitation, if you want to ask me anything feel free, I’ve worked with families in your situation more times then I care to remember. I know im a stranger but sometimes it’s good to talk to someone who doesn’t know you. I notice a lot of talk of depression, bare in mind he might not have been depressed, though it is likely, it could have been any of a number of things.
The best piece of advice I can give is to keep a positive attitude but be realistic.
Remember feel free to pm me if you want to ask or talk, I’ll gladly give you my number even.