Currently there is no confirmation when deleting a slide. This can result in it being accidentally deleted. As far as I can tell, there is no way for the user to self-serve in recovering a slide that has been deleted this way. CTRL-Z works to undo changes / content removal which has been done on a slide itself, but cannot recover a slide delete.
Although the slides are numbered sequentially in the course itself, they seem to have unique identifiers in the URL which would suggest that maybe they just get de-linked and tagged as deleted in some database table column. This to me would suggest they're not actually gone, though trying to access the URL of a deleted slide (as expected) didn't work.
Are there any plans to offer users the ability to recover accidentally deleted slides? If there were a "trash can", this could be combined with functionality I suggested in https://community.bridgeapp.com/ideas/1992 to copy the deleted slide back into the course regardless of when it was deleted.