I'm so sorry for your loss, new york new york. I lost my mom suddenly two years ago and it's really rough. Sometimes it still feels like yesterday. She'd only been gone a year when we moved to London and I was really worried about "abandoning" my dad, even though my brother and his family live closer than I did when I was in the US. Right from the start, though, he started planning trips to come over several times a year. He's semi-retired, so has quite a bit of flexibility.
Basically, at any given time, there are plans for me to go home or for him to come here in the pipeline. To be honest, it helps both of us a lot.
No question, there's still guilt and worry. There was guilt and worry when we were in the US, too, though. I suspect the worry goes both ways.
He's done a really amazing job of staying social and accepting invitations when they're offered, even if it means he's the odd one out. These days, he's mostly settled into a life that resembles his life with my mom as much as possible. He'd never want to move here permanently (well, with us, nothing is ever permanent!) and he would feel hideous if we moved nearby just to be nearby.
Day to day, I keep in close contact, calling once a day, and I really keep him involved in what's going on over here. For most of my post college life (15 years), I lived 8 hours away. On some level, an 8 hour drive vs an 8 hour flight isn't that different.
Rant away. It's a really, really shi!tty time and I'm sorry you're going through it.