Dry Bibs are the way to go when pairing up a dry top. Be sure to get the kind with a relief zipper though or you will pee yourself scouting a big drop
I have never used dry pants and can't say with any real knowledge that you could flip over and drown, but the theory seems well justified. I guided years on the Upper with dry bibs mated with a dry top and have been fine, although on a tough swim it is nicer to have the full drysuit. I actually wear neoprene pants and a dry top creeking since I am looking for added protection as well as insulation if I take a swim. Kinda old school but it works.