Sorry to hear about your sister.
Not the same at all, but I moved here after learning my uncle had cancer (we are very close as he’s been like a father to me) - that being said I’ve seen him 4 times since I moved 5 years ago and he and my Aunt are considering a once in a lifetime holiday this year they’ve wanted to do for years. He still has the dreaded C but is currently stable.
The fact is, whilst we are far away geographically, depending on where you are you can be in your front door within 26 hours - I actually came back for 2weeks to look after my mother when she had an operation and it really isn’t that far, more so in your head.
Skype is also a wonderful thing that means you can be in touch daily at a reasonable hour to you both.
Of course, family comes first, don’t have to choose between one and the other in my experience.