This is a really tricky situation so I'll try and explain it. FIL married when he was young and had three children. Years later he met MIL and he left his wife and children. The children were in the picture until DH was about 6 when they suddenly disappeared and DH didn't even know they were his siblings until last year. We found out when they wrote to us, which was quite a surprise for DH. There is no relationship between FIL and the first three children and there is a lot of anger from the children and they say that he abandoned them because MIL made him. He has also refused to have any contact with them or his grandchildren. When he learned of the email to DH he was very angry and "dealt with it" and we haven't heard anything since.
Now FIL is ill, old and frail and doesn't have long left and I am upset with the idea that he has children and grandchildren out there who won't have a chance to make peace and say goodbye. I also believe that he would like to have that chance too but MIL is a real battleaxe and would never suggest / listen to such an idea from him.
Is this a situation which should be left alone or one which could be made better before it's too late?