I guess what I was looking for was an answer to whether or not it is a design feature to be able to create monitors on folders that don't exist. I was planning to ensure that new monitors have valid stat objects on creation. That way, if the directory is gone by the time the monitor attempts to create a monitor object for the folder, it will throw an exception and not end up hanging around.
If, however it's intended that a monitor could exist for something that doesn't exist yet, I don't think that my plan can be used to mitigate the problem. I think then that the only real solution would be to filter out non-existent paths from within the inotify callback.
Filesystem.Monitor is supposed to be able to monitor not yet existing paths. No such monitors should however have MF_AUTO or MF_HARD.
/grubba