Well, Frankie Campbell died a short time after getting brutally ko'd by Max. That was a comfirmed kill. The other death that Max supposedly caused was Ernie Schaff. Funny thing, Max didn't even offically knock out Schaff, he won a majority decision. But the bell had rung while Schaff was getting counted out in the last round. Back then, the count ended at the end of the round. Anyway, Schaff goes on to fight Primo Carnera and collapses in the 13th, from what, no one could figure out. The crowd booed as Schaff's life slipped away. It was specualted rather widely that Baer was responsible for Schaff's eventual demise, although it can't really be proven.
Yeah, Baer could crack, no question. Had one of the all-time best chins in the HW division, too. If he had been more dedicated, he could have been an all-time great, and likely would have been Louis's prime rival for supremacy in the late 30s and early 40s.
Baer has an Iron Chin and a lethal right hand. He also had a lot of hand problems late in his career or he would have had even more KO's than he did. There are only a handful of former Heavyweight Champions that have 50 KO's or more.
Baer was to easy to hit to ever rival Louis. Anyone who could be hit easily would lose to Joe regardless of how motivated they were and regardless of how good their chin is. Easy pickings for the Brown Bomber.
Baer could have cleaned up on the Uzcuduns, Braddocks, Sharkeys, etc. to establish himself as Louis's main rival. In terms of ability, of all the fighters of the era, only Louis was better. Whether a trained and motivated Baer could have beaten Louis is, of course, a matter of speculation. But I think he'd have a damned good shot. If Schmeling could knock Louis out, Baer at his best certainly could.