Santana and Cron had very similar xwOBA in 2018. It's likely they both see a lower xwOBA in 2019 as Cron had a huge jump vs his career and Santana is on the downside of his career.
That said, the trajectory of 1B in the last couple decades is to peak at 28 (which Cron just did) then level off thru age 30, at which point they start to slowly decline. That means Cron will likely outhit Santana by a smidge over the next two seasons.
Santana is a much better fielder. He is also a better fit for the roster allowing you to platoon Austin or Astudillo.
In John Bonnes, gun to me head fashion, I'd take the bet on Santana being a better player over the next couple seasons, but it's negligible. If the Twins can strike a deal that is essentially payroll neutral over the next couple seasons then consummate it. Maybe Cron, a C+ prospect and $25mil.
If we take Swarzak back in the trade, I suspect Dipoto goes for it. What's the sentiment on Swarzak. Is he washed up? He had a steep dropoff last season and I have not looked into why other than BABIP.