Come rain or shine means to get something done no matter what the situation is (could also refer to actual weather conditions).
1. Irrespective of how many people came for the concert, the organizer would go ahead with it come rain or shine.
2. Battling a mild fever, the tennis player decided to take to the court come rain or shine.
3. Dark clouds loomed ahead but the enthusiastic fans thronged the stadium entrance, wanting to see their teams play come rain or shine.