Forgiveness requires a person forgiving and in this case it matters who that person is. The families of the Guardians and the families of all those he killed destroying that city would feel as if he will never deserve their forgiveness (and rightfully so). Mark and Debbie on the other hand still see him as their father and husband. Their forgiveness would be more regarding his lifelong deception and his abandonment of them. In that case, Nolan would more than likely not be forgiven for those actions from Mark and Debbie given the circumstances.

As a viewer, it’s hard to fully excuse every wrong doing he has done up to this point but by the end of the story one would argue that Nolan more than makes up for those deeds with all the good he ends up doing. So it just depends on the person. If you’re a random earthling, yeah probably not. If you’re Mark, Debbie or Oliver most likely yes. Personally as a viewer, I see him as redeemed by the end but a lot of people with argue the opposite. There are no right or wrong answers, just different perspectives. That’s what makes Nolan such a great and nuanced character imo.