Is it a certainty that the airport would have to be shut down without them?
In trying to understand those descriptions from 11 years ago
https://www.toronto.ca/wp-content/u...ter-rwy-08-26-extension-assessment-052413.pdf
(although I'm no expert, and may be incorrect), it looks like:
-doing nothing and not adding the Runway End Safety Areas (RESAs) would mean only the smaller 9 passenger planes would be allowed.
-construction would be required to add the RESAs extending out into the lake to maintain the current operational length of the main runway.
-using the ends of the present runway for RESAs would shorten its operational length, thus reducing the maximum allowable take-off weights of the Q400 planes, decreasing their fuel load and eliminate some destinations. Do we know which ones?
I would guess if they could no longer fly to Montreal, New York, Chicago, etc., Porter and Jazz/Air Canada Express would likely cease using YTZ.