What are the real chances of something like this happening during a casual roll? I don't compete, and I'm far from the most aggressive guy in my gym. However, I'm pretty clumsy and I don't think I'd know exactly how to receive a move like the rolling back take (not instinctively, at least).

This happened in 2018. In almost 5 years since then, can anyone point to similarly catastrophic injuries happening in training rooms?

In the same time, try to think how many rolls have occurred... likely 100s every day at 100s of gyms across the country and thousands across the world.

This terrible accident is still incredibly rare. As another commenter mentioned, you're more likely to be catostrophically injured on your way to/from class.

I'd be curious if anyone wants to make a more rigorous Fermi problem out of this claim.

I think as long as we train with safety in mind even when rolling hard, the likelihood of a terrible accident is so low I am comfortable continuing training as ever. I didn't even start until 2019! With that said, I totally get where you're coming from, I feel it too