Please take what I'm about to say while keeping this in mind. I'm an outside observer, and more importantly, I'm in a calm state of mind. I'm not experiencing the emotions one might be in this situation. But I do have a lot of experience with being distraught over online interactions.

I know I'd feel abandoned and betrayed if it happened to me. But I also know I've clammed up and gone dark many times in the past as a defense. I can't speak for the hypothetical person in your scenario, but like, I've been guilty of doing what they did because I was like "I don't deserve to bother other people, they don't need to see me, I'll block them so they I won't show up for them anymore". I'm just saying there's a whole bunch of reasons to be ghosted.

As far as other people who may still have connection to the person who pulled away from you... I don't think it's appropriate to "call them out". What have they done wrong? What are they doing wrong? They may have relationships of varying degrees with this person, but this situation isn't their responsibility. If your relationship with this person can heal, then it's up to that person to reach back out to you on their terms. If that happens, you'll be absolutely right to tell them how you feel about things, and also it'll be up to you if you want to repair things with them.

Roommate? Uh, that's a wrinkle in the situation I can't process. Sorry, I don't have advice on that.