Keep deleted murals for 30 days available for recovery (like a recycle bin). Deleting a Mural can't be undone without assistance from the support desk.
As it just happened to me - deleted a folder but was too fast acknowledging that any murals within are deleted too - gone.
That made me contact support (very helpful guy Andrew btw!).
If you calculate the time and effort it takes to restore murals that way (if successfull), it should be considered a win-win for both, mural and the customer.
Btw.: it would be beneficial to implement a change that if a customer deletes a folder, the murals it contains are archived by default, not deleted!
I also recently have to go through support to recover a mural, and it wasn't a painful process, Ben from support helped me in no time. But I think a self-service recovery area / recycle bin would be great. Another approach that Trello takes is not allowing direct deleting, you first need to archive, then delete from there. It is in a way a recycle bin, dame result, different approach.