I found it very dangerous to not be able to recover a deleted project. Think if someone found your password to login into webflow and your username. Now he decided to delete all projects for fun and logout!
You login and discover that months and years of work are gone forever!!!
What a waste of time and money, I think you should reconsider how you manage the deletion of projects, permanently should not be an option!
Like this morning I decided to cleanup my project folder to only keep the final version of my website project. By mistake I choose the wrong project, deleted it forever and lost days of work!
I imperatively suggest that you add a delete website project with backups and the backups could not be deleted. Then no hacker or human errors will destroy forever your work!