I don’t really get the SR system that’s used for ranking, so if a match ends up being 7 - 89 is the SR for all teams just 7? Also, if a team is disqualified does the other team receive an SR of 0? I read the manual, but couldn’t understand it too well.
There is no such thing as “SR” in the context of determining rankings. If you are referring to “SP”, or “Strength of Schedule Points”, then they are defined as follows in the Game Manual:
Thus, if a match ended with a score of 7-89, then both alliances would receive an SP of 7 for that match.
Your second question is answered by the definition of Disqualification, quoted here and bolded for emphasis: