I would suspect a lot of good quality caches owned by cachers who are active in the game, feel their caches are worth saving, and are willing to put some work into their cache placements and maintenance. If were were gambling on a percentage, I'd say 24% would remain. I would do my best to keep all of mine.
It would be sad to see a few older caches go which are great caches but their owners are just no interested. But overall I think it would be a good thing and would support it.
While many caches would be archived, I imagine a new breed of placements would evolve. Caches would rarely be hurriedly placed, which I believe is a common denominator to lesser quality caches. Possibly fewer caches would be placed by hiders not interested in maintaining them, since they would have someone to answer to. I think cachers would feel more at ease caching in public areas knowing that permission was given for the hide. It would still not be perfect, land changes ownership - sometimes without notice, some hiders would "cheat the system", and some finders would still violate conditions required by the landowner, but it would still be a step up IMO.