I've thrown my bag in the water to prove to myself that it floats (it does!!), but haven't intentionally kept in the water for a longer period of time. I would assume it continues to float as long as there are no holes. :-)
We have several of these bags for shore bags and ditch bags on the sailboat. They have been in the water and we have tested them for flotation and keeping electronic equipment dry in storm conditions and they work well. However, we have only had them in these conditions for 15-20 minutes (the time it would take to get from the boat to a life raft) and without anyone hanging on to them for flotation.