I've actually had the experience of being washed off a flooded causeway, but in a 4x4 TK Bedford truck.
Had a settlement cut off by flood waters and they needed fuel for the bores and generators.
Going over was OK, sort of, but after refueling everything the truck was lighter.
The rear axle went first and the truck followed in reverse.
Fortunatly, it jammed up against some trees so it just become a big recovery mission. Took more than a Jeep to get it out though.
In hindsight, it should have been a warning to me when I couldn't get anyone to ride with me.
I'm a slow learner though. Since then I have crossed a few flooded river crossings, fortunately with no adverse consequences.
That doesn't mean that I'm not bloody stupid for trying them though.