I have two different versions of my site: a desktop version, and a mobile optimised version. That is, for the same URL, the server renders different HTML for different user agents. I had been using vary header for this scheme as recommended by Google.
However, now I want to move the mobile website to a single page application.
I want to know if Google stops seeing anything on my mobile web version but the desktop version continues to work as it is, then how would the search rank be impacted given that mobile web gets more traffic than the desktop version. How would the vary header come into play