Many many what-ifs.
Maybe it wouldn't have made any difference, as the pilot of the less damaged machine didn't seem to have the other one sighted at all prior to impact, but what strikes me from that rear pax video is how he (understandably) whacks the pilot on the shoulder to presumably draw his attention to the converging flight paths, but that gets the pilot looking to the right and inside at the exact point where he may have had a chance of evasive action. Probably too late at that stage anyhow, but just a sad observation.