The odds are that your packs are at least as buoyant as you are, unless they are loaded with scrap iron and water.
Probably true, although at the time both hands were fully engaged in getting out of the silt and the packs were dragging us down faster into the river, we came pretty close to going under and that was when they were nearly jettisoned. Floating would have been fine but it was the dragging under that had my attention!
It certainly focuses the mind when experiencing something like this, and finding ETS and all the contributors has improved my skills/kit selection - which can only be a good thing.
ATB
Moab