We're rapidly approaching the point, if we haven't already reached it, where social distancing is not practised in most situations by most people.
Exactly. The official guidance to socially distance, with certain compliance obligations placed upon businesses etc, may stretch into late Q4.
In practice, behaviours started to change in May when people sensed (correctly) that the worst was over, and I believe there will be a tipping-point when schools and colleges return. These establishments will not - cannot - enforce social distancing, and nor can the public transport that serves them. A great number of white collar staff will return to their offices at around the same time, and after a fortnight of performance to 'the rules', I'm pretty sure that watercooler gossip and barely-distanced meetings will resume.
By October, in going about their daily lives most people will have forgotten the guidance exists, and exactly what it says that's relevant to the particular environments they encounter.
I think there are some customs which won't return for the forseeable, such as shaking hands by way of greeting and 'air kissing' female acquaintances. Ditching these is cost-free and, frankly, desirable for a great many. I reckon those stand-up business receptions where you juggle a drink, finger food and networking conversation at close quarters will also be banished until 2022: thank goodness!
In the exit phase, people will do what they're comfortable with and the official guidance will fade in significance.