By that point almost everyone will have been exposed anyway no matter what quarantine measures we take. At this point we're just trying to slow the spread, but essential activities have to continue (food, transportation, utilities, healthcare, infrastructure, military, emergency services, etc) and so everyone involved in those is going to act as transmission vectors. Once the vast majority of people have been exposed, any further widespread quarantine measures will become moot.

The airline industry is going to be crippled though, and might still be operating at limited capacity in October.

What do you think 80% normal will look like? I'm currently planning a small (30-50 people) event in October and I'm trying to figure out if I need to postpone/reschedule.

I'd just assume it needs to be rescheduled into 2021. Should group gatherings resume before the end of the year, which seems unlikely, it seems a safe bet that turnout would be rather low just due to people not wanting to risk it. On top of that, we're most likely going to be neck-deep in a pretty painful recession (at least) by then.

It's probably not a good idea to hold such events before a vaccine or an effective treatment are available. Neither is likely in the next 12 months.

I was actually wondering about Christmas yesterday. I moved across the country a decade ago and go home for two weeks at Christmas each year. Assuming there is no vaccine by then (which seems to be the most likely case), I was wondering what was worse: 2 4+ hour flights and the airport time or taking the 3 days and 2 hotel stays to drive (or even sleeping in my car at a rest stop if that is even allowed). And that's all assuming there aren't travel restrictions in place in 8 months.