It depends how you deleted them. Did you delete them via the Library window? If yes, then they're gone! You'd need a file recovery utility to recover them.

If you deleted them from the dwnlds list on the search/dwnld window then it's not a major issue. You can search & re-select them to dwnld (generally better not to use the resume function in the library - they can often start from 0%.) To know which ones are missing you can make a list from your incomplete folder & compare it.