Well...I'm a service manager...so I have to train/babysit a few idiots...I mean newbies once in a while.
I've seen the affects of gas in a diesel engine many, many times as you can imagine. I work with mostly tractors and larger commercial mowing products. 90% are diesel engine powered.
Just last week, we hired a guy that didn't know how to tell the difference between diesel and gas. He poured gas into a little 23 HP diesel garden tractor. Started and ran fine. Idled perfect. Smooth, quiet, but it smoked a little bit...just a little. As soon as he gave it throttle, it smoked even more and started to miss. That's how I knew he had put gas in it.
Another story goes along with it. Years ago, I was working with a guy to get a 225 HP inline 6 turbo diesel on a tractor up & running after a rebuild. Someone had filled all the diesel cans with gas by mistake and the tech doing the work ASSumed that they were all diesel, and poured in 10 gallons. Tractor started and ran, and in fact, it didn't run too bad. Now, he's an older guy that's pretty stubborn....and swore up & down that the injection pump had a problem. So, we got out the testing equipment, dyno for the tractor's PTO, everything. Started it up, watched some pressures (and all was fine...except manifold pressure). Started to load it down and as I was watching the manifold pressure increase steadily he came off the tractor and started running. 'Course I wasn't thinking and figured he was coming down to watch the gauges. I'm standing there watching things and listening, and next thing I know, I am feeling a little bit of hot water hitting my arms...then a little more, and finally, I start to see steam from between the cylinder head and block. You could literally see the head lifting from the block, wasn't much, but it was happening. It finally lost compression & quit running of course. Guy that was inside the cab said that the tach got to 3700 (max RPM was supposed to be 2400) and he ran out.
Moral to the story, if it's supposed to run on diesel and you put gas in...the least that would happen is that it would run bad. Injection pump also required lubrication...and the diesel is oily and lubes the pumps...and we all know that gas doesn't lube too good. Worst thing that would happen...see the story above.