Urgent advice required...

Great stuff!. Listening to this is suspect it may survive the swim without the sock. Why not go and do a training swim without the sock and see if it survives? In my experience it clings on for a day or 2 but then, after a shower you can sense it coming adrift and you can pull it off. The final bit of magic, which I did not tell you about, is that it often seems to speed up the healing of the blister. As you know, zinc oxide is the old wives treatment for nappy rash. Sometimes, old skool stuff works! Glad it worked for you.