Hello,
My understanding is that right now you'd have to reach out to Microsoft (and only in a disaster recovery situation) for them to restore data.
Instead, for the implementations I've done, I used the "copy company" feature if I need to test something. If you search "Companies", then you'll come to the page where you can add/copy/delete companies. Highlight the company you want to copy and choose "copy" in the ribbon- then give it a new name.
As for any master data, if I import it and it isn't looking good, I've also used the Edit in Excel function to highlight everything I don't like, delete them and then "publish" it back to the company. If these are initial imports (no transactional data yet), then you shouldn't have any issue mass deleting in Excel.
Hope this helps,
Brittney