Why would a Falcon 9 failure set the BFR back six months? The teams working the BFR parts are probably not strongly involved and could just continue working.
It would set them back somewhat, but I don't see why it would be that long.
"Return to flight" activities appear to be a big distraction for the entire company, for example the previous 2 failures caused Falcon Heavy to slip a lot.
It would set them back somewhat, but I don't see why it would be that long.