Oh Denise, you must be absolutely gutted. And having to put a brave face on it must make the pain even harder. I do feel for you. My older daughter lives 15 minutes away by car but I hardly ever see her or the grandkids. She seems always to be so busy, as do the kids. I've had fantasies of lovely family Sunday lunches but I've pretty much given up on that. I also feel that if I ended up in hospital and they called her, she probably wouldn't answer the phone – too busy!
My other daughter lives 400 miles away in Scotland and, despite the distance, she is much more accessible and reliable. At one point, there was a chance that she might stay in Australia with an Australian boyfriend. I would have found it so very hard, but it didn't work out and she came back to the UK.
I don't know if something like this might work for you but my niece's daughter, partner and their first baby (my niece's first grandchild) live in New Zealand – even further away than Australia. My niece (now 70) lives in East Sussex. Her plan is to spend six months of the year out in NZ, six months here. She is in the fortunate position of being able to buy a small house out there in addition to her home here. She also has NZ citizenship as her dad was a Kiwi. For now, it seems like a workable plan but I don't know how much she'll be able to cope with that long flight as she gets older.
I know it's nothing like the same as being with family in person, but technology does offer better links than we one had. There's Zoom, FaceTime and WhatsApp so maybe those options will give you some small comfort.