One of the central purposes of RCU is to decouple the updater/writer(s) from the reader(s). It doesn't matter to the writer if there is still a reader "out there" using the old version. And it likewise doesn't matter to (most) readers that the version they have is now old.

What is delayed is the actual destruction/deallocation of the RCU-managed objects. Nobody cares about that delay unless the objects control limited resources (in which case, RCU is likely a bad fit) or there are so many objects and/or they are so large that the delay in deallocating them could cause memory pressure of some type.