I'm so sorry to read about your estrangement b0dhiTree, my heart goes out to you. We have been estranged from our son for over 4 years now. Haven't seen our eldest GC since the age of 8 months, now aged 5, and have never seen our youngest of 14 months.
Sadly, there are many parents in this situation; there's another thread on this forum specifically about this about living with estrangement and moving forward, you may like to take a look.
We too were extremely close to our son and his wife's manipulation has resulted in the same sad result. As Starlady has said, you are not alone and although it's upsetting to know that others suffer as you do there can be some comfort in the knowledge that others too find themselves estranged, through no fault of their own.
You ask how you can cope, not easy to answer because we are all different and so all have different coping mechanisms but for me the first step was not even taking one day at a time, but a couple of hours at a time.
I spent the first year in tears and hardly going out. I'd stay up late listening to sad songs and sobbing and get up late every morning because there seemed little point in getting out of bed. My dear husband Mr. S. cried a lot too but bless him, managed to drag himself up and out every day to go to work.
Now, when I look back at that first year I have absolutely no idea how we came through it with our sanity in tact. It takes time b0dhiTree, you need time to grieve for the daughter you've lost and for the GC you've never known.
As for recovery, I don't know if any of us ever will really recover but what we can do is make the most of what we have, focus on the people we love who love is in return. We hope for the day that we can remember our AC before they left us with a smile, and not just our tears and the terrible pain that living without them brings.