if you do plea agreement to knock C Felony to A Misdemeanor, but are discharged unsuccessfully from probation, does original charge stand?

It would depend on how the sentencing was handled and how the plea agreement was written.  If your plea was that you plead guilty to a Class A Misdemeanor, then it wouldn't impact how the case appears on your record.  If your plea was written in such a way that upon completion of probation, the State agrees to allow the charge to be treated as a misdemeanor, then you may be still stuck with the original charge.  You should have an attorney look over the plea deal for you.