Does sp_droparticle @force_invalidate_snapshot=1 invalidate the entire snapshot?
The idea of a snapshot is a point-in-time copy of the entire publication, so once you make a change that affects the snapshot, it's no longer valid in its entirety.

From here:


  Dropping an article from a publication involves dropping the article and creating a new snapshot for the publication. Dropping an article invalidates the current snapshot; therefore a new snapshot must be created.


Once you call sp_droparticle and invalidate the snapshot, the publication cannot be subscribed to again until a new snapshot is generated.