'He won't take more than his fair share'
- sorry, but please don't consider that feeling at all. Completely dismiss it, even if it's likely to be true, and treat the whole transaction as you would if it were a business transaction with a person you don't know.
You presumably thought he 'wouldn't' dump you when you'd just been bereaved and had an accident, right?
You don't need to get arsey about it, but simply get three agents in to value it independently for a start, agree a price with him, and then tell him, quite unemotionally, that as you are going to also have the cost of finding a new home, moving your stuff etc., and he won't, as a result of HIS decision, then you will expect a % more than that 50%, or you won't agree to being bought out. I'd make it around a grand - cost of moving, the fact that you now won't be paying off a mortgage and he will, cost of rental deposit etc.
Also, think about NOT being bought out if you think the house is going to rise in value in the next few years and you would have trouble getting a mortgage on your own. It's your investment too, above and beyond being your home. He can't actually take it off you, and if it makes financial sense, you could keep it.