Will my defense lawyer be able to plea bargain / negotiate my Missouri DWI charge down to another (lesser) offense?

Perhaps.  Negotiating a client’s case with the prosecutor is something that your Missouri lawyer can advise you about.  Sometimes a plea to a lesser type offense is possible.  Sometimes a suspended imposition of sentence is possible.  This SIS can result in the dismissal of the DWI charge upon successful completion of the program requirements.  In some cases, your only option will be to plead to the DWI / Excessive BAC offense or take your case to trial.