I don't think he should be banned for the rematch for speccing out in the last 30 seconds of a game that wasn't close... it's not like him speccing out in any way affected the outcome.
All of the match suspensions relating to speccing to avoid death since I've been back, dating back to Season 14 now, have been in lopsided matches from what I can remember. We've still banned all of the offenders for their next match. And I see no reason why a repeat offender shouldn't be banned for multiple matches.