It’s working just fine here.
Please note that it’s a 2 step process, patterned after the way WordPress does pages and posts.
From the main admin side sheet list page, if you click on “Trash”, it just puts the sheet in the trash, but it is NOT deleted yet. That sheet just won’t appear on the front end anymore.
If you then click on the Trash text link at the top of the list table of sheets, you can see all the sheets that have been put into the trash. From there, you can either restore or delete the sheets. If you choose to delete a sheet, at that time the tasks and signups for that sheet will also get deleted.
Also, when a sheet is in the trash, you should not see any signups on the list of user signups. I have also tested, and this is working properly here for both the user signup list below the main list of sheets, and also if you are using the separate user signup list shortcode on its own page.
Are you running the latest version? If so, perhaps you have some sort of conflict with another plugin that is messing things up, because it’s working just fine here and I have had no other reports of anything similar to this with the other 2000+ active installs.
