DELETED
https://support.avast.com/en-eu/article/Use-Antivirus-Virus-Chest
Hope that helps. I don’t have any files in my virus chest. 
(No money in my treasure chest either.)
DELETED
It simply states that once deleted they can’t be recovered.
Well for a start they aren’t sent to the regular trash-can/waste/Recycle bin, they are pretty much gone. Even using a file recovery tool is highly unlikely to be able to recover anything.
Files in the Avast Virus Chest are also encrypted and renamed, so don’t really have much chance to even find them (before deletion) searching on the filename from outside the virus chest.
General advice is:
- There is no rush to delete files sent to the virus chest, a protected area, where they can do no harm.
- If it were a false positive and you delete in haste you have time to repent at leisure.
- Wait a few weeks (to ensure there is no adverse effect on your system) and (if not) scan them again from within the virus chest before deletion.