If anything, if the healer role regained braincells and could no longer face role through content it would change things for the better. That is, assuming it is well done. What I am about is based on the best case scenario.
Healers will become more popular but still remain smaller than dps in population. Old healers would return, new players would play it, and more content creators might actually pick up healers if they get interesting again because that would make decent topics for content. New players pick up complicated dps jobs all the time. If anything, new players will continue to try healers even if they regain much of their old kits (with tweaking for modern game content) and mechanics. It would put a new lease on life for older content, especially if the devs finally begin tweaking kits at lower levels to be engaging and balanced to not melt everything out of sheer potency.
The tole would slowly regain respect. The developers, if they did this and did it correctly would regain some respect from players (especially if the maintain that level of care).
This isn't the full picture, obviously. We still would have role encroachment to deal with (WAR's absurd sustain).