Hugs, Dilly! I know this is hard for you! It would be for me, too, or most any parent, surely.
But as PPs have said, there are so many ways of staying in touch today. And you can have some wonderful visits.
I think the posters who spoke of crying in the shower, etc. have the right idea. IMO, it's normal for a parent to grieve over the "lost" (changed) relationship, but they should do it privately, and put on a happy face for their AC and CIL. In fact, IMO, it's a good idea to try to actually see the benefits of the move, as you seem to be doing.
Also, I agree, DIL may think this is a good way to get DS away from the influence of his drinking friends, and, yes, his dad. Unfortunately, I'm not so sure this will work for long. If DS is really an alcoholic, he'll find drinking friends there after a time. He may really need to get into AA, and she, into, AlAnon.
Anyhow, it will take some adjusting to get used to this move, both for them and for you. But I'm confident you will adjust. Keep us posted!
Army horses loose on London streets