Souza and Cole is too much to give up for only one year of Ben Zobrist. I am a big fan of Zobrist but he isn't the kind of guy that a team will sign and give up a first round pick for so in effect we would possibly have a Kendry Morales situation on our hands were we lose a bat, don't get the extra first rounder, and still lose two of our top 10 prospects.
If we are going to give up multiple top prospects in a trade it needs to be for either an elite talent or someone with more the more the 2-3 years of team control otherwise it just doesn't make sense.
If no one signs him to the qualifying offer it's almost certain he would be back with the Nats at the QO price, or face being out of baseball, losing several million dollars, and coming back mid-season in no shape to earn his next contract, which is what happened to Stephen Drew and Kendrys Morales this year. I don't think you'll see many guys sitting out until mid-season from now on.
Ben Zobrist is coming off 4 straight seasons of 5.4 WAR or higher (so we can disagree over whether he's an "elite" talent), and is signed for 1 year @ $7.5 million. One season alone is worth probably $20+ million in excess value over his contract price. To that you add either a 1st/2nd round pick, or another year of Zobrist at $15 million or so, which is still a bargain. Either way, the total excess value Zobrist would provide, with a draft pick or a second year, would likely be $25-30 million. If you think Souza and Cole are worth more than that, that's okay. I disagree.
