I have diagnosed a leak (after many hours of testing and examination) in the line that runs from one of the main drains to the large second outlet from the skimmer. I have read in several forums that this line is to act as a secondary source of water for the main drain in the event that they become plugged so that the main pump does not run dry (assuming water is above bottom of skimmer intake). I have now capped off the outlet from the skimmer, leaving only the one smaller opening accessible for water return (and vacuum) to the main pump and filter. Everything seems to be working well and there has been no water loss in past 24 hours compared with 4" loss in 24 hours before capping. The pool is a vinyl liner, in-ground 16' x 32' pool with attached overflow spa and is 4.5 years old. I'm located in Toronto where we can get very cold winters. My questions are these:

Will leaving this skimmer outlet capped cause any damage or performance issues with the pool?
How can I make a permanent fix to this situation?
Is this main drain-skimmer line required at all?
Can it be winterized correctly if I eventually repair it?

Many thanks.