Not really. You don't really know until you work out the numbers, there being so many variables. Although experience and instinct gets you most of the way there if you have the experience.
He was out of ground effect but was effectively at or above the airplane's absolute ceiling . During his forever takeoff, he used ground effect to gain a bit of surplus energy to allow him to, more or less, zoom climb to about 50 ft, where he found himself with no surplus energy left, on the peak of the power curve, but slipping to the backside of the power curve. The rest of the flight was slowly consuming the speed margin on the back side of the power curve until he was about to stall and mushed into the trees. You can see his pitch attitude slowly increasing bit by bit during that whole phase. He didn't need rising terrain; he put himself into a trap whose only escape was to return to ground effect and eventually land.
The biggest red flag, beyond the sheer length of the ground run, is the part where he lifts off and settles back onto the ground. If that happens when you are at your normal liftoff speed, the airplane is screaming at you to give up. If he had lots of hours in that Stinson, the instinct that comes from familiarity should have been sufficient to recognize the red flags.
The final red flag is simply the lack of acceleration from thrust above 20 feet or so; instead of zooming to 50 feet on surplus energy, you should feel the plane pulling you faster.
Aside from those clues, the other obvious one is doing the little bit of performance math where he could have determined that he was already at his absolute ceiling in those conditions and needed to wait until a time when the air was cooler. But discarding all that, the skipping takeoff and sluggish acceleration should have been enough warning.
When I was bush flying on floats, in a not-very-rocket-like Cessna 180, there were many times I would be taking off with a very heavy load, on a very hot day, where the performance was marginal even at 1500 ft asl (density alt maybe 4 or 5000 ft, enough to make a float equipped 180 pretty doggy). I'm on a lake whose length I can only estimate, and I can only estimate my all up weight (coming back from a pickup from a camp).
I would set a reject point, usually about half way down the water run using a shore line landmark. If the airplane had the performance reserve, you could tell right away as it would come off the water and you could feel it accelerate smartly once clear and would immediately start to climb. Too much of sluggishness there, and I'd fly along in ground effect to see if it improved and put it back down right away (with the shore line looming) if it wasn't accelerating once at about 30 feet or so. Then back to the dock to off load that outboard motor they insisted they bring along.
Sometimes a customer would insist I take all his stuff, and I knew it was way too much, but sometimes you have to find a tactful way to say no, so I would say "let's try it", and go step taxi down the lake with the power reduced (the customer can't tell that you're only at 23" of MP) until the opposite shoreline was looming, say "we won't make it; you don't want us to crash into the opposite shore do you?" Back to the dock to off-load non-essentials, and no complaints to the boss.
