Do I have to reboard if I lost my promotable status due to not updating my ERB?

According to Milper Message 11-233, no you do not have to re-board. Hope this helps.

C. IF A SOLDIER IS REMOVED FROM THE PROMOTION STANDING LIST BECAUSE THE UNIT
FAILED TO UPDATE A PREVIOUS APFT THE SOLDIER WILL NOT BE REQUIRE TO BE RE-
BOARDED. UNITS MUST USE THE INTEGRATE FUNCTION IN THE PPW TO RETURN THEM TO A
PROMOTABLE STATUS ONCE THE APFT SCORE/DATE IS CORRECTED. FAILURE TO UPDATE
TRAINING/PERSONNEL DATA DOES NOT CONSTITUTE A BASIS FOR AN ARC. REMEMBER
THERE CANNOT BE A GAP BETWEEN APFT DATES.

Have you asked your supervisor? Your NCOs should be the first ones you ask before posting a question like this in a forum.

SGT promotions are not centrally managed like SFC and above. Just have your S1 shop update your records and you should be ok. But, because this is managed at the unit the unit may have their own rules. So talk to the S1/PAC as to what the unit rules are. I would be surprised if they made you re-board. But each unit comes up with their own rules.