I have no problem with caches being archived when the owner has moved on from geocaching, as a new cache will generate renewed interest in the area, and I think the whole of geocaching in general is benefitted by the dynamism of new caches. Turning over new caches keeps interest fresh.
There are some situations where adoption is desirable, however, such as granfathered cache types. If these are not adopted then we will gradually lose all those Virtuals, moving caches and caches placed in locations that would no longer be tolerated by our masters at GC.com. (I think we can blame MAGIC for this last problem).
The only difficulty is that there is no mechanism in place for taking over a cache without the owner actively giving it to you, and if they’ve lost interest in caching then that won’t happen and the cache will be lost.