I will say it again. Encore une fois: I don't know where you guys are flying but in Asia and most specifically in China, there is always someone talking on the radio. So an awkward silence of more than 1 minute and you know something is not right as it's too quiet to be true.
Then it's loudspeaker on first and only then we remove the headset not the opposite way around. Same as when you set the flaps you always check the speed before not the other way around. It's a question of discipline. At least I expect that if I'm doing that mistake that my colleague won't. So very unlikely to happen as it's done like this on every single flight.
And last but not least, I would rather taking the risk of losing communication for a couple of minutes than flying all the time with strong interference and most probably ending up with altitude burst as you can't clearly understand the radio when both the loudspeaker and headset are tuned on at the same time. A 320 drivers flying with ANR headsets will acknowledge that. if it was not making this annoying interference I would keep the loudspeaker on for more redundancy but it's jut too unbearable that echo. Lol
The scenario you present, not saying it's impossible but I think I have more chance to win the lottery than that to happen. 3 unlikely events to happen at the very same time. What are the odds? Nom de dieu! xD