This general goodbye letter is great to use when moving away from community, friends, neighbors, and family.
Dear {Recipient},
I missed you at the {farewell party, dinner, cake in the office break room, etc.}, but I wanted to make sure to say goodbye, even if it is only in writing.
It's been great {working with you, hanging out, etc.} for the last {length of time}, and I'm sorry it has to end. But luckily for us, we live in the age of technology, which means I'll only be a click away if you ever want to talk or hang out or whatever.
I'll definitely miss {the company, neighborhood, apartment building, etc.}, but I'm trusting you to hold down the fort.
I'm sure we'll talk soon.
Best wishes,
{Sender}