If they do that it will be the night before the trial. I suspect that they are so invested in this case they they cannot back down now.
They will more than likely double down on all the courtroom parlor tricks that got them this far and hope for a juror or two who lies on the jury applications.
All the state needs, in order to get a hung jury (assuming Nelson does not find a preponderance of evidence in favor of justified self defense) is one liberal juror, or one black juror. Compared with Zimmerman, the state has infinite resources, and can keep going indefinitely.