The salary is whatever. Toronto was always going to tank so cap concerns couldn't have been a factor since they were never going to sign anyone of value this year.
As for the virtues of tanking, that's hindsight talking. Looking back, of course it was worth it, but it certainly isn't worth it if you're looking at Tkachuk right now. All tanking got you was a coin flip chance at drafting top 3. So looking back at the trade, Kessel was traded for a good prospect, a certain late first round pick, and a slightly better chance at coin flip odds at the draft.
All I'm saying is that I'm shocked they fell over themselves to get rid of him. It felt there was no patience exercised and for a rebuilding team where getting the best return for your assets is pretty important. The front office has been very savvy this past year, except for this trade.