You can say he's clearly on the decline, but the very same arguments were made about Verlander and actually about Cole Hamels (speaking of effect on 2018, not the residue of his contract) and the wisdom or ill wisdom of acquiring those guys respectively.
Depending on the acquisition cost, it's a relatively safe gamble. There is no commitment here. You are really only risking what you give up. And your upside is you have really good pitcher who needed better health or perhaps a new perspective.
I personally don't see the Giants getting 50 million dollars of surplus value out of one year of Bumgarner, and I would walk away from that deal in a heartbeat.
I wouldn't give more than Newk or Fried straight up. I'd be hesitant with Newk. I honestly don't care much about Fried and doubt that his trade value is much higher. But I would expect the front office to have shopped one or both around the league to figure out that value and to make decisions accordingly.