Your so lucky to have friends that are there still. I would try your best to keep in touch, even with a short reply by text. You never know what the future brings
I would not block. In the past I have simply explained that between chronic depression and autism it is difficult for me to stay in contact. I value them, but I am not good at maintaining my end of the relationship and I hope they understand. They all have so far.
Don’t burn a bridge if you don’t have to. Friends are too few as we age. Keep what you have while you can.