So, I have many opinions on this.
I think the move to online will be detrimental to learning, but also ineffective at slowing the spread. Once students return, they will mix and socialise anyway, the less lectures = more time to go out and get drunk/high.
The idea that students will stay in specific "bubbles" is ridiculous to me. Firstly, almost every second/third year & postgrad have accommodation completely outside university control and that has already been sorted out by students privately. There will still be challenges for those running halls, as rooms have already been assigned (with many rooms at different pricing tiers) and accommodation providers tend to group similar-ish personalities together to avoid conflict. (There also tends to be a huge amount of people moving flats, when they don't get along with other flatmates.) And also, you're telling a bunch of teenagers who've just moved out of home to not party and not have sex with each other. Some of the crusty bean-counters who came up with these ideas probably haven't had a drop of hormones in their blood for the past decade.
Now, we can either live in cookoo land and pretend that with online learning the university can distance itself from all accountability, but let's come back to reality. Students have already paid for housing, made plans to move and many are already moving in. Once they're here, they'll either be locked in their room away from all their friends and family, with only the odd zoom based lecture or freshers event to stop them from going insane, or they're going to go out and party/**** and risk spreading covid.
So the sensible thing to do, is set up testing on campus (some kind of tent where you can pick up or drop off kits), encourage students who do invite others over to keep track of who they have been in contact with using social media/messaging, distribute cheap masks and sanitiser across campus, make sure all spaces are ventilated and then get students back in to study. Sans the larger lectures, students should be getting the same seminars and practicals, as these are where the true learning happens.
I'll add a comparison to state my theory. You have abstinence only education vs safe sex. One sticks its fingers in its ears and pretends it won't happen, the other is proactive and makes sure to minimise risk when it does. Funnily enough, the second actually results in less sex, because kids don't feel like they need to rebel...
We can either stick our fingers in our ears and pretend we can put it all online and make it go away, or be proactive and minimise risk in ways that aren't completely detrimental to the learning experience. Everyone's only going to spend the extra time drinking at Spoons or sharing a spliff outside a Maccies anyway...