I have my son's email address and though the last time we sent him a message he answered with a legal-sounding 'cease and desist' request, I think I would send him a message if something momentous happened. For instance his Grandad isn't too well, and if he were to pass I would want to let him know, though how do you send bad news -cold- when you don't know what's going on in the the headspace and life of the recipient?
The last time he cut us off, he gradually got back in contact and he eventually returned home as an alternative to being put in some kind of lockdown accommodation but as it just went belly-up again I feel he knows it's better for both of us to be independent of one another's emotions. I trust him to go out there and learn to be a human being, and to come back to us when he is capable of functioning independently and rationally - if he can't, I cannot do anything to help him (though am prepared to help financially up to a point ) and he can only hurt me more, so I am basically planning to be, what's the word, unresponsive? until I see some real change. He's still young, and I still have hope. If he ever makes contact I will let you all know! Sorry this isn't much help as it's only been 6 months, but I would definitely try to leave a neutral channel of communication open if you can. Hugs!
