2nd link delineates their fate. They did not survive. I agree their only hope was to swim for it the minute the water started to rise. Very few people would have the presence of mind to act that swiftly and decisively.
Three things keep coming to mind as I think about this incident.
1. Could they have survived in the cave as the water rose?
2. Did they make a swim for it thinking they would drown in the cave?
3. Were they swept out of the cave?
Compared to the rest of the world I spend a lot of time in canyons and on rivers either rafting, kayaking and canyoneering, this type of scenario is always in the back of my mind.
Several years ago my wife and I and another couple were standing in line at the backcountry desk in Zion to get a overnight permit for the Narrows hike. Before we got to the counter I told my wife and the other couple that I just didnt feel good about the hike and spending the night in there. I have had gut feelings about things before while rafting or skiing and have avoided being in bad situations listening to my gut. We decided to do a one day Subway hike instead. That night as we lay in our bags the clouds moved in and proceeded rain and thunder all night long. Reports from the rangers the next day was that hikers in the canyon were safe but had to scramble to higher ground as the water rose.
Listen to your gut, it's usually right.