I think it will mostly come down to health -- not so much his, but other people's.
For Sano, when he does come back, it will be with a rehab assignment. With several days off along the way. A minor league rehab assignment can be as long as 20 days. With the amount of time he's had off, it's hard to imagine something less than seven days, even if he crushes the ball. Much more likely is that it will take most or all of the 20 days. And unless he's crushing the ball in the minors, it's hard to imagine them clearing a 26-man spot for him on the shorter end of the 7-20 day range.
Unless someone gets hurt, which is where the first part of the health comes in. If someone does get hurt, then you can clear a spot for him. If not, I think he stays in St. Paul for the full 20 days. More on that later.
Unless someone gets hurt on another team. If that happens, and if he's crushing it in St. Paul, then maybe there's a smidgen of trade interest on him, IF the other team doesn't have a minor leaguer of their own. But it's hard to imagine receiving much of anything for him in a trade. Teams won't view it as 1.3-1.4 seasons of control, because there's virtually no team that is going to pick up the option at that cost. And someone's going to have to pay the buyout. If the Twins make the other team do that, the prospect return is even smaller. It seems more likely that the Twins would have to send cash to cover the buyout, if not also part of this year's salary.
That's a lot of "if" and "unless," making me think it's very unlikely that a trade happens.
Which brings us back to the rehab scenario. There's no point, and no savings, in a DFA, other than being able to keeping someone else in his stead when he's required to come off the rehab assignment.
So it's back to a Twins player's health, and I'm guessing they wait as long as they can to make a decision. That means doing as much rehab as you can before you start the 20-day clock, UNLESS someone gets hurt or starts to slump. Then, they can use the whole 20 days if they need to, making the decision on how he's performing vs. however someone with options is performing, calling him up when there's a sense that he can improve the team. By then, yeah, if nothing has opened up and he continues to struggle, you can go ahead and consider a DFA, but realistically, that's not going to happen before the trade deadline when you consider that the rehab hasn't started and can last 20 days.
And related -- given how Kirilloff, Arraez and even Miranda have played, given how poorly Sano plays first, and given that they will want to Sano from a re-injury, it seems very unlikely that he will get even an inning of 1B, either in rehab or when/if he comes up.