Ooooh 'eck. 😬I know they leave, but if my 2 left for another country, I would very upset. I know it's their life and they need to make their own way and so on, but I would find it very hard to deal with them both leaving for another country.
Mine (both mid 20s,) moved out a few years ago, (after they finished uni.) Both living with partners, and in their own home now. But they are only 15-20-ish miles away, and I can be with them - and they can be with me - within 20-25 minutes. (If we suddenly needed each other.)
DH has a work colleague (woman in her early 50s) whose son left to live in the far east 5 years ago aged 23 (only child...) She nearly had a breakdown. Especially through lockdown when she didn't see him at all. Went a whole year with no visits, just facetime and skype. Even now, she still cries some days because he is no longer there and has no plans to come back.
May seem like an extreme reaction to some, but her feelings are as valid as someone who isn't bothered! I know some people cope fine, and also, we have no right to decide our DCs lives, but I really would struggle with my 2 moving overseas/1000s of miles away.
A lady who lives near me has 3 children - all in their 20s, and all went to uni - 2 boys, 1 girl. They live 300, 400, and 500 miles away, (the 500 miles away one lives in Germany!) She says she misses them terribly, and wishes that at least ONE of them lived within 20 miles. Her reaction is not as extreme as the other lady with one son, but she looks sad sometimes when she mentions them.
They make their own way though, and we should be happy for them that they are independent. But it is a wrench when they leave, and as I said, I don't know how I would cope if my 2 left the country. I have never said this to them, and would not stop them/say anything/try to make them feel guilty, but deep down, I would be crushed if they moved abroad. Especially 3000+ miles away!
It's nice to have no childcare responsibilities and for your kids to be making their own way in life, but in my heart and soul, I desperately miss the days when they were little children, and I was the centre of their universe. They love me as much as I love them I know that, but most of the time, I feel like an outsider looking in on their lives from the outside.
I know several families with 12-20 family members living within 20 minutes walk of one another, including adult children and grandchildren - and they see each other 2-4 times a week, and I do envy them a bit. This was my life as a child, as a teenager, and as a 20-something... I had around 15 or 16 family members within a mile. And I do miss this.
We had lots of get-togethers, parties, and BBQs, and all met at the social club every Friday night with a few neighbours. And we had some lovely big happy family Christmases, with the house buzzing with visitors and people popping in and out all of Christmas day and Boxing day! Loved it. 
(I see my adult DC twice a month by the way... And I have no grandkids at the moment...) As I said though, mine are still only 15-20 miles away, so it's not too bad I guess.