Remember that almost no one is good at maintaining relationships
Email, texts, and phone calls go both ways and I’m guessing they haven’t called you either. We are all busy and, let’s face it, life gets in the way and people move on.
So, instead of thinking that it’s done and how awkward it’d be to reach out to someone from the past, I want you to change your thinking. Remember the great working relationship you once had or all of the good times you spent together. Realistically, if you called them out of the blue, it would probably be a nice surprise!