Cubs are going to have an interesting offseason. They lose Lackey, Arrieta and Wade Davis. They have around $140M already committed to next year's team...and that amount varies wildly depending on how much you think Russel, Bryant and Hendricks will command in arbitration.
The luxury tax next year is $197M, and I assume the Cubs will avoid going over that if possible. So that leaves them with somewhere around $50-60M to come up with 2 starters, a closer, and bullpen help. I think you have to assume Montgomery will move into the rotation, as they won't be able to afford 2 top end starters and 1 top end closer.
The Cubs traded away or promoted all of their young talent and currently have ZERO prospects within the top 100. So there's no immediately help on the way from the minors.
Schwarber needs to be in the AL. He can't stay in the outfield. Not sure what his trade value might be.
Jayson Hayward provided less than 1 WAR this year. He will make over $28M in 2018 and was barely better than a triple A replacement player in 2017. That stings and suddenly looks like one of the worst contracts in baseball.
The Cubs should still be the heavy favorite to win the division next year, but their future is suddenly concerning. Lester and Zobrist are entering their decline years. These young guys are going to continue getting more and more expensive as they go through arbitration and eventually hit free agency. Their window is still wide wide wide open, but I think it may end up being a much shorter window than some people think. They might be lucky that the rest of the central sucks right now.