Since you're searching for deleted files, you're best bet is to search in unallocated areas of the harddrive, I really can't remember if R-studio offer that kind of search

With that specific regular expression we're trying to find the header of a wallet.dat file, if your search returns some hits, you need to figure out your self where that piece of file ends and export it as a wallet.dat file.
As with deleted files, they can be somewhat overwritten by other data, as this area has been marked as empty for the operating system to write files.

This is why it's so important not to use such a harddrive anymore, as data can be written just in the area where important data is stored.