It was the Queen's advisors who advised against the HI/HO. I don't think we know what Charles's stance on it was; he would have accepted what his mother wanted/was advised to do. But anyway, he's in charge now.
A cancer diagnosis focuses the mind on the future. I doubt that as a father he would want to leave this earth thinking that his sons were not on (at least) civil 'colleague' terms. I think Charles would like it if duties could be shared; Kate has also recovered from a cancer diagnosis, something that has surely focused her mind on prioritising her health and her children. Andrew is out of the picture.
I think peace will be made between Charles, William & Harry. I think the way is being paved for Harry to HI/HO. Meghan will probably continue on her own path in the US.
I would actually love to see this happen and I think public opinion will sway towards acceptance of a HI/HO for Harry. I reckon they'll keep testing the waters, Harry will smile and be charismatic a lot and the general public will be happy to see his back - or at least accept it.
I will obviously eat my hat if I am wrong! But I think it's happening.
Edited to add: I think William and Kate will want to keep their children away from doing any duties for as long as possible and if Harry returning to share the workload helps with that, they would go with it.