Buttonville Airport has been sold to developers and will be closing within 5 years.

http://www.citytv.com/toronto/citynews/news/local/article/98355--buttonville-airport-sold-to-cadillac-fairview

Buttonville is the 10th busiest airport in Canada. Where will all of these aircraft and flights relocate to?

In my opinion, this virtually ensures that the Island airport will never close - regardless of Porter's future.

Rumor has it that the SENECA flying program might relocate to Peterborough.
Other airports are available for the other operators but are not - in my opinion - suitable. Brampton and Burlington -runways too short for the larger business aircraft operators, Downsview - too close to Pearson and therefore restricted access due to Pearson traffic in the vicinity.
Oshawa & Hamilton - too far to service the "business" demands. Pearson could certainly handle most of the business (jet) traffic but that still leaves a significant amount of other traffic to be accommodated. Guess where?

I can see new hangars being built on the south side of the Island airport to accommodate the influx of new aircraft. This idea was already presented by Sypher-Mueller when they discussed the addition of more Commercial traffic so it is not a new idea or my suggestion.

Stay Tuned.

Take Care!
Joe