Once the District Attorney files a criminal case with the court, only a judge can dismiss it. Since the arraignment is your first appearance before a judge, it's hard to imagine how a case would be dismissed before that, absent some extraordinary circumstances.
That's also how you would know that a case was dismissed... because a judge would say, in open court, that the case was dismissed. The clerk would make a notation in the court records, which you could review to be certain it was dismissed.
However, I don't understand why you think the case is going to be dismissed. In order to file a case, the prosecutor must have a good faith belief that the defendant has committed a crime. You're unlikely to just walk into the District Attorney's office and convince them to ask the judge to dismiss the case, and the judge won't discuss the particulars of your case at arraignment.
A theft conviction can have lifelong consequences. I'd strongly encourage you to talk with a lawyer who can guide you through this process.
As I read your answer you haven't been arraigned yet. If that it is the case there is always the possibility the DA may decide not to file a charge. In my county, SF, cases that are not going to be prosecuted are discharged the day of arraignment. Once a case is discharged the DA still has a year to file assuming the charge is a misdemeanor.
If the case is not discharged and you are arraigned then Mr. Marshall is correct in his answer.
Your question concerned dismissals. If no case has been filed, there is nothing to dismiss.
As Mr. Kaman notes, in most misdemeanor cases, the District Attorney must file charges within a year of the offense. (If the offense is a "wobbler" that can be filed as a misdemeanor or a felony, the longer period for felonies would apply.)
Sometimes the DA has not filed charges by the date a defendant promised to appear in court. However, that is not a dismissal and charges could still be filed later.
With a few exceptions that don't apply here, once a misdemeanor case has been filed and dismissed, the DA cannot refile charges.