"My problem is going from weekly visits to being cut off indefinitely."
Once again, as a GP caregiver, myself, I can just about imagine how painful that must be. The time I spend with my DGC (dear grandchildren) has lessened, recently, now that they both go to fulltime school and, in the summer, day camp. And I know it will decrease more as they get older. But if they were suddenly torn from me, entirely, I know it would hurt me very deeply!
Ordinarily, I would suggest finding other ways to fill your time. But it's not as if you had them several days a week and could use the time to get household chores done or pick up on an old hobby... well, unless you work during the week and could use the weekends to socialize with friends, etc. I know little or nothing will make up for missing them, completely - I'm just trying to think of some things that might help.
Some estranged GPs swear by volunteer work. If that appeals to you (and if you're not already doing it or even if you are), please note that GP.com has established the GrandCorps (see the very top-left of this screen) to help hook up GPs/Seniors/Boomers with volunteer activities in their vicinity that interest them.
BUT if this rift only occurred, recently, it's possible DIL is still just angry and when she calms down, she'll reach out to you again, if only for a few weekends of babysitting. Chances are the 4-yr-old, especially, will ask for you, from time to time and her mom will, eventually, relent. (When I said the kids are "ok," I meant simply that, fortunately, I think, kids bounce back emotionally, faster than adults, in most cases, not that they don't ask for you or want to see you.) Unless this last incident was, somehow, the culmination of an ongoing issue, I don't think this separation is necessarily permanent. And even if it was the latest in a series of problems, I still feel there's some hope here. You may not be asked to watch the kids as often as b4 - DS and DIL may decide they need the weekends to spend time together as a family - but it's very possible, IMO, that you'll be sought out for childcare, once a month or every other weekend - not what you were used to, no doubt, but better than nothing.... Just a thought...