Once a sustainable varroa resistant apiary is established, new queens and colonies can be raised quickly.
The varroaresistant.uk team has identified a strong heritability of varroa resistant traits through queen lines

Some treated colonies would be able to manage varroa themselves but their varroa resistant traits are bring supressed as the treatments supress the varroa for them. But the majority will be mite susceptible colonies that would perish without the treatments.

The key observations in a varroa resistant colony are uncapping of worker brood, chewing out of infected pupae resulting in pupal exoskeletons on varroa insert boards, resulting in low mite counts as the breeding cycles of the mites are interrupted.