If you're trading Jake to get back future prospects, then it makes the most sense to trade a guy like Schwarber to get as good a SP as you can to replace Jake. It'd be great to see Soler headline a package for a young arm who has potential of being sub 3 ERA/200 innings but that just isn't going to happen. So if you traded BOTH guys, it would make some sense where as trading one of them does you nothing really. If you trade Jake and keep Kyle, where are these prospects going to play with Kyle, Russell, Rizzo, Bryant, Contreras firmly entrenched in your future lineups? And if you trade Kyle and keep Jake, do you really want to rely on 1200+ PA from Soler/Baez/Almora at two positions next year? That's a lot of risk both in skill/ability as well as in injury in the case of Soler.
To me, I'd wait for the DBacks to fire Stewart/La Russa, make a buy low on Shelby Miller as a future 3/4 and then hope you can continue to find value in other places. To be perfectly honest, the highest upside pitcher I can imagine being in the organization is already here and that's Dylan Cease. I don't think a team would give up a higher potential arm than that even in a deal for Kyle simply because that kind of arm is valuable that you won't really risk that all on Kyle + other prospects.
I mean there is no real problem with the Cubs giving Jake fifteenish million next year and then him playing out the year as a top 10 SP in the NL with potential to be top 3 while you're trying to win a WS. This year, the Cubs had a ton go right with the rotation both in terms of performance and injury; not so sure I'd just give up a top 10 SP because he wants a lot of money. If he wants a lot of money, offer the QO, get the pick, then go sign his replacement in FA at about 75% of the cost and hope the system can you give you a guy who's 90% of what Jake is.
Wouldn't surprise me at all if the Cubs go after Tyson Ross this off-season because his stuff fits perfectly with what they want to do and if you have him for the year, the team would be better prepared to offer a long term deal with regards to how healthy he can hopefully stay.