I was estranged from my parents for 15 years. Literally lived around the corner from them. My mother dropped down dead. I went to the funeral helped carry the coffin, but then was ignored and not invited to the wake. 5 years latter my father had a stroke. I visited him in hospital every day and we kind of mended the broken bridges. However, he was discharged 10 weeks latter and suffered a massive heart attack the moment he got home and died.
I don't know the reasons for the issues you and your son have. But from someone who's parents cut them off, mend those bridges, if possible, before time catches up with you all.