I accept that some MPs could be abroad or just sick. However 50 is a tad high and I suspect their absence was just more than a coincidence.
As you say Labour will not call a GE until they have to but this vote was the first shot across the bows from his own MPs. The fact that he had to call back MP's who were campaigning in Scotland and issue a three line whip ordering his MPs to support him is telling.
Apparently he is considering asking Raynor to rejoin the government as her tax affairs are about to be cleared up. She would be a mug to join a sinking ship better to sit it out on the back bencher's until the Titanic has gone down.
She's like the injured player, the longer they are out the better the fans believe they have become.