Hi Jon,
If you've lost an estimate in your books, there's a few ways to find it.
You can go through the audit log (it doesn't take as long as you think)
You can find the account or product that was on the estimate, and select "run report" on the product or account, and it will bring up the estimate.
Find the customer, likely the estimate will be saved in their customer account field.
I normally go for the audit log method, i go to the dates i think i did it, and just slowly search.