2020 valid answer.
They will not be able to view the files but their files are NOT deleted. They can still find and recover the files they own
Steps to find and recover lost/orphaned files from Google drive
Log in to Google drive.
Find lost files by clicking on this link: FIND MY LOST FILES
by placing on the search bar:
Recover files by just right-clicking on the file and selecting
It is safe to delete files from your Google drive not owned by you.
Still, you should notify the owners on how to find and recover those (orphaned) files.
Following the above steps even removed files by anyone (created or uploaded in a shared folder owned by someone else) can always be recovered by the present owner of the mentioned files.
Noone can delete uploaded or created files in Google drive but the owner of the mentioned files.
When searching the site other similar questions like: Does deleting a file from Incoming folder in Google Drive delete the original file?, What happens to files when deleted from a shared folder which has been added to their Google Drive?, How to view orphans in Google Drive, In Google Drive, does ‘remove’ delete file? It says it’s still accessible by collaborators, Where are files that I shared with someone going after he deleted them come up as well. I find those either confusing to me or quite old and possibly outdated.