The disused prefix is for keys "which are no longer true as a result of the disuse". Here, if even, rather disused=yes would be applicable which is used "in case when being "unused" does not negate a feature's primary function", like a disused building.  A path is still a path even if it's illegal, and it still could fulfill this function. (The question would then be what the difference between no access and disused is.)
If it really is completely overgrown, visible while standing at the barrier, then yes, it can be marked as abandoned.
But I wouldn't make a conclusion just from time passed too quickly. I have passed many former paths (mostly unmapped) in Sihlwald that still looked well. And I recently accessed a path at Uetliberg blocked for safety for two years now and I couldn't really see any overgrowth taking place at all.