If that drops r below 1 long enough it would have to right?
This seems especially hard to do though, since compliance would need to be nearly universal. You could potentially wipe out influenza and the common cold at the same time too though potentially.
Some individuals may stay infectious forever. E.g. Typhoid Mary[1] was quarantined twice, and the second time she remained isolated until death. (Thypoid fever is a bacterial infection, but I assume something similar can happen with a virus.)
In addition to the others, there'd be a long tail of few infections before it's actually wiped out, and during that period I expect too many people to just stop caring about masks for it to actually get eradicated.
This seems especially hard to do though, since compliance would need to be nearly universal. You could potentially wipe out influenza and the common cold at the same time too though potentially.