The endgame is to figure out the least cost sustainable measures of getting R0<1 until we have a vaccine or treatment safe enough for people in high risk groups to take.
The question assumes this has already been done: "single cases here and there, maybe even 0 cases".
It seems to me that the key question at that point is, if there are no active cases--everyone exposed to the virus who is still alive has either never developed symptoms in the first place, or has recovered from whatever symptoms they had and is now asymptomatic--is there still a risk of spreading the virus further?
You're missing my point. I'm not saying that R0<1 implies "single cases here and there, maybe even 0 cases". I'm saying the converse: that "single cases here and there, maybe 0 cases" implies R0<1. Which is obviously true. And the scenario posed in this "Ask HN" question assumed "single cases here and there, maybe 0 cases", so if that implies R0<1, and it does, then the OP's scenario does assume R0<1, even though it doesn't say so explicitly.