Speaking as an ex-CSRO, I would say most private pilots have little or no appreciation of sea survival issues. Getting out of the aircraft and into a dinghy is something seldom planned and very rarely practiced. I would suggest survival chances are quite slim, especially when the water is cold and the procedure un-practiced.
Having said that, I do like to relate the experience of a colleague of mine who used to ferry aircraft for a living before deciding flying airliners was safer. He was ferrying a light twin across the Pacific when an engine failed about 600 likes out of Hawaii. Being heavy with ferry tanks, the aircraft slowly descended as they limped back to safety, finally ending up in 'ground effect' hopping over waves. Eventually they got it wrong and clipped a wave which sent the aircraft nose down into the sea about 350 miles away from land. The impact was very violent and my mate broke his nose on the coaming, but luckily remined conscious. He and the other pilot clambered over the ferry tanks out of the rear door, taking the dinghy with them. Once inflated, the tailplane of the sinking aircraft split it in two. My mate had taken a second out of date dinghy along and he dived into the sinking airframe to retrieve it. He managed to get it out and once inflated, only one chamber held pressure. They had the 'grab bag' which had an early 406mhz beacon. Subsequently, a B737 was diverted to find them and actually found them - a passenger spotted the dinghy after the Captain had made a PA asking everyone to look out for them. A Coastguard C130 later dropped them a new dingy and supplies and about 24 hours after ditching, they were picked up by a helicopter dispatched from a Coast Guard cutter.
He makes the point that they were extremely lucky to get recued. The second dinghy saved them. But they struggled to get into that dinghy, were tired and hypothermic when they eventually did, despite the Pacific off Hawaii being relatively warm. Both had survival training. This, and their preparation saved them, but on reflection he wished they had been wearing immersion suits. . When they got into the Coast Guard dinghy, they scoffed most of the rations in one go! This was also the first ever recue using a 406 beacon.