What are the possible exit conditions of the Coronavirus Lockdown loop?

Being locked in is not pleasant. There is also a little guilt of going out of the house, especially for walks, even if there is virtually no one around. Could we be increasing the duration of the lockdown by being careless? Uncertainty about the duration of the lockdown is stressful.

So, I thought that if I were writing a program for the lockdown, what are the conditions which would determine the exit condition for the lockdown loop for a particular region with no person entering or leaving the region:

1. There are no new cases emerging.
1. The virus stopped spreading for no known reason. This is the way The Plague by Albert Camus ends.
2. The virus has disappeared from the community thanks to the lockdown.
2. The community has developed a herd immunity.
1. If the lockdown is perfect, how can the community ever develop herd immunity?

If the region has not developed herd immunity and the borders of the region are opened, we will need to make sure that no infected or potentially infected person enters the community. Hence, testing and quarantine of each visitor will be mandatory.

If in spite of all efforts, an infected person enters the community, the lockdown will need to be imposed again.