See, here's the thing. The DA doesn't get to determine whether or not someone goes to prison. The most they can do is either try the case or make a deal that a judge doesn't necessarily have to accept.
The key to any trial is what's called voir dire. It's the part of jury selection where the DA and the defense counsel get to talk to the jury pool, try to educate them about the legal issues surrounding the case without going so far into it that they stray into the judge's territory, and ultimately, get some background information about the kind of jury pool they're facing. In my home jurisdiction, both the DA and I have a certain number of peremptory challenges, where we can kick someone out of the jury for essentially whatever reason we want to, as long as we're not stupid enough to say it's because of their race or gender or some such protected category. Now, if I'm defending an NFL player from a charge of domestic battery where I know the alleged victim is not going to cooperate with the DA in the case, I'm going to be able to raise the opportunity cost of trying my client to intolerable levels. In pretrial meetings, I will be openly musing about how extensive the media coverage is going to be, how easy it will be for me to win a budget-busting motion for venire (where the jurisdiction brings a complete jury pool from another jurisdiction), how if the DA or the cops screwed up even slightly, then my client has the resources to sue the relevant agency into bankruptcy civilly, and the dismal conviction rates when domestic battery cases go to actual trial. If it's an ADA, I will be going over the ADA's head to his boss and talking about how she's not going to have a chance to get reelected when her ADA loses in a very public matter. When it comes to jury selection, I will pick the oldest jury I can that's chock full of married people, because they disproportionally don't give a shit about domestic battery. I will have a barrage of expert witnesses, all of whom will require that the DA's office obtain the expensive services of counterwitnesses. If the DA does not call the victim as a witness, I will move for dismissal of the case at the summation of her case, and I very well might win. If the DA does call the victim as a witness, I will have the critical witness in the DA's case doing everything she can to undermine it. In all likelihood, I will obtain a not guilty verdict for my client, and I will be whistling a happy tune walking out of court, thinking about how I've just generated enough business that I can finally close on that vacation home in Hawai'i. And the most important thing is, the DA will know all of this is true before our first meeting.