My best friend from college went radio silent for almost three months last year. I kept meaning to text her, but life got busy and I figured she would reach out if she needed something. Turns out she was in a really bad place and felt completely alone. That silence almost broke our twenty year friendship. Now I set a reminder on my phone to check in every two weeks, no matter what. It feels forced sometimes, but it keeps that door from swinging shut.
Doubt that most friendships need that much work to stay alive. People drift apart all the time and it's usually fine. Your story @the_lucas is the rare case, not the rule.