They would probably not take the PR hit of dumping Santana for no return and 50% of salary, but he's still a pretty good player. If they were motivated to move on from him there are probably deals to make where you still get something (prospects, a reliever) for him.
As with Herrera, Santana's also disappointing on defense. These guys were both up for Gold Gloves last year (I think Santana even won one of the other awards) so for them to fall short of expectations while also struggling with offensive consistency hurts (and makes it harder to justify putting up with Hoskins' defense in LF, because that was supposed to be balanced by Santana being a better defensive 1B than Hoskins).
I'd be surprised if Santana got any starts at 3B but it does give them something else to do earlier in a game. They'll also have Florimon and Crawford soon enough.