If there's anything that you think that I missed, under-or-over emphasized, or that'd be useful to fisherfolks in a more likely scenario I hope you'll chime in.
The only thing I can think of is that it's hard to overstate how much worse having waders filled with even a few liters of water can make any swim in moving water. One of the more stunning fatalities in my peer group came about when the guy that everyone felt safer paddling with due to his skill, experience, and granular knowledge of the local runs wound-up flush drowning in a drop he'd run dozens and dozens of times before when the legs of his dry pants (he was wearing a dry-pant/dry-top combo) rapidly filled with water when he was getting recirculated in a hydraulic, and if overwhelmed the bouyancy of his PFD. All this despite the fact that there were two full-tilt Class V boaters on the scene trying to effect a rescue.
The odds that anything other than a full-bore drysuit will keep water out if someone's getting trashed in a nasty hole are pretty low, but one step I've taken in the wake of hearing many stories about water-filled waders/pants, etc is wear a drytop over my waders if I'm on a float where the temps/gradient/etc are considerable enough to warrant that (rare).
If I think there's a reasonable chance that I might be doing some heavy wading, I bring along a beefed up wading-belt out of a waist-gasket that I cut off of an old drtyop (Pic below), and jf conditions warrant it I pull it up and secure it near the tops of my waders. It won't keep all of the water out either, but I've tested it out vs the standard issue waist-belt and it dramatically reduces the amount of water intrusion if you go full immersion.
Probably not something many people would want or need, but it's worked for me.