Trash and restoring deleted items
Deleted leads are recoverable for 30 days before they are removed for good.
Deleting a lead does not remove it immediately. It goes to Trash, where you have a window to change your mind before it is gone for good.
Restoring
Open Settings → Trash to see soft-deleted leads. They are kept for 30 days; restore one and it returns to your pipeline exactly where it was.
Deleting for good
From the same page you can permanently delete an item before the 30 days are up. That cannot be undone, so it asks you to confirm. Anything still in Trash after 30 days is cleared automatically.
What is kept, whatever you do
One thing never leaves on its own. An invoice with money recorded against it, and a contact holding one, are kept as your financial record: the permanent delete refuses them and the 30 day clear-out skips them, so they stay in the Trash until you restore them. Compass tells you this when you delete the record, not later.