I can see totally legit arguments for paying him next year and retaining the rights to his services for the following campaign. Or, one would hope he'd be amenable to a two year contract of some sort that gives the team a bit of a discount for that last controllable year if they stick by him. Who knows?
As for Leake, I'm taking the other side. I really--REALLY--like this trade for what it is. They gave up essentially nothing, got $750k in international signing bonus money, and received three plus years of a ~2.0 WAR starter. That's not a #5; that's a rock solid #4, average MLB SP. Better to address areas like this before the offseason sets in so that the FO can narrow focus. If he produces ~2.0 WAR then he's well worth the money, and he solidifies this team's most glaring weakness now and going forward. This season would have played out a LOT differently if Smyly hadn't come up lame before opening day...
Look at Leake's FanGraphs page. 2012-2016 saw between 176-214 IP per season, 30-33 starts, xFIP 3.49-3.91. His walk rate is in the Iwakuma range, 1.53-2.30 BB/9 over the same period...you know who his stat line looks like to me? Doug Fister. More fastballs than Doug (~70% FB+CT for Leake's career, ~60% FB for Doug's) and a few more MPH on Leake's fastball compared to Fister's, but Fister had the angle and delivery to make his look faster than it was.
You could look at this as a trade for a Doug Fister doppleganger who's under club control on a perfectly reasonable FA contract for another 3 years--and we gave up nothing of immediate consequence to acquire him. Remember: a 100 ERA+ is average, right? A 29 year old ML-average SP on a reasonable contract is essentially impossible to acquire on the FA market.
I'm not saying the move should blow the doors off the place, but isn't this a great piece of the puzzle to acquire for the next few years? His velocity *is* down a bit, and has been trending that way for a couple years, but with that kind of control it seems like a good bet that he'll produce his paycheck.