I think we're supposed to find the ending more hopeful than the modern reader is likely to do. He's been accepted by his father, he's reconciled (sort of) with his wife, and he's decided he's not to live: that's three quarters of the problem solved!

Having said that, now that I've read another Lindop book, she may also be the kind of writer who enjoys endings that will haunt you with a sense of incompleteness.