If the files are removed from the database only, they will show up in the 'removed' database as long as the file remains at the location MC expects it to be.
If you subsequently delete the file, or move it, MC will notice that and drop it from the 'removed' database.
If you have "Ignore Deleted" turned off in auto import, it will just re-import deleted files, and thus remove them from the 'removed' database.
If you remove files from the library that are in a location not covered by auto import, then those should remain in the 'removed' database as long as the file exists in the location it was at at the time it was deleted.
At least, that's my understanding of how it works, from my climb up the learning curve some years ago now. I have not tested any of the above in a long time, but I'm also unaware of any changes in this area. That does not mean there hasn't been mind you
-marko