I said total rebuild if Lamar leaves and I stand by it. Lamar is the most unique QB in the league. Without him it changes so much. It would be a huge blunder for the Ravens to hire someone based on a Lamar led offense, but then have Lamar gone. The entire system would have to be thrown in the trash and then... wait for it... rebuilt.
Not if you find a qb with a similar skill set and that seems to be getting towards being the norm now anyway. A new coordinator is likely going to change some things even if Lamar is retained anyway.