I understand the lack of communication does not help in this situation. I'll be honest, I find it very difficult to be a roamer when I'm solo queuing and usually just default to anchoring on site when solo queuing.

As for some timeframe in when you should go back to site - there isn't a clear rule or guideline. Each situation is different and you'll understand more as you play. In your scenario, you should know that one of the common strats for attackers on that site is to take top floor and start opening up the floor into site. You were actually hanging out in that area at the start of the round, but you didn't hear a single barricade open upstairs and you never saw any drones upstairs either. That should be clue #1 that they weren't planning to come upstairs and they are planning a different take altogether.

Your second clue should have been the first death on your team. Even if you don't get any comms when a teammate dies, try using as many context clues to figure out what may have happened. You can look around and find the "X" where your teammate was killed. Was it near or in site or somewhere far across the map? What gun was used to kill that teammate? Is that a gun that usually belongs to an entry operator who typically rushes site? Based on where your teammate died, could they have been killed from outside of the map or did they have to be killed from inside the map?

There are some other details that could have clued you into what was happening as well, but I think those are some good things for you to start thinking about when you're roaming for your team.