A total tear down and rebuild could work, and could take less time than many people would think.
Goldy, Pollock, Castillo and Segura would net quite a prospect haul. I can easily see getting the following level and quantity of prospects for these players, as is, without having to absorb any of their salary:
3 A grade
3 B grade
3 C+ grade
Now...at the same time you look at Greinke:
If you trade Goldy, Pollock, Castillo and Segura you are saving about 25 M in 2017 and close to 30 M in 2018, and 15 M in 2019.
Thats 70 M total savings.
You gotta spend that money SOMEWHERE, right ? And you are not going to spend it on free agents.....so what do you do ?
You absorb 70 M of Greinke's money, and suddenly he looks like a REALLY affordable pitcher to almost every team in the league. And for that 70M + Greinke, now you are buying 1 A grade and 1 B grade for that 70M
Suddenly you have infused your system with
4 A grade
4 B grade
3 C grade
Now.....because you have traded Greinke, and moved the remaining portion of his contract off the books, (beyond the 70 M you absorbed), you STILL have money you can eat on Tomas' contract and maybe use that to add to the prospect haul
And of course you have a high draft pick in 2017 and most likely 2018 as well.
By 2019 most of your haul of A&B prospects in these trades has played at least some time in the majors and a few are hitting stride, and your farm system is stocked further thanks to your high draft picks.
You are competitive by 2020 latest, maybe 2019 if you are a little lucky, and are positioned with one of the best farm systems in the industry, AND due to the escalating nature of the TV deal you signed, you have a lot more money to splurge on free agency to fill in where you need to heading into 2020
Really the only way you don't embark on this course is if you believe the team is a few tweaks and a few good breaks away from being able to sustain a few good seasons in a row with a winning record. But believing that isn't enough., I don't see that evidence for that, and someone would have to present a very strong case to convince me that the team is really that close.