Not easily... depending. I alway rename them with an X_ in front of the original name. That way you can wait until you have run a DDR and check were they are used before the final delete.
If you still have the table instance on the Relationships chart, you can reconnect to the original table and reinstate the relationship matches. All should be ok from there.
If the table instance is gone... you will have to rebuild everything which relied on that relationship.