I wonder if someone has marked his card for him? Alternatively, since there may yet be some epic constitutional moments ahead, perhaps he's decided to store up a little powder and keep it dry.
Spurious Historical Precedent Alert: the whole thing reminds me of Chamberlain in May 1940. Everything, and most particularly his personal authority, crashing down all around. Remember the crucial step he took: when he went to the Palace, he advised the King to call for Churchill. It could as easily have been Halifax ... Yes, scary days ahead.
Mrs May, who seems to have a carefully prepared speechlet for all contingencies, may well have dusted off Chamberlain's final address to the Commons:
Everything that I have worked for, everything that I have hoped for, everything that I have believed in during my public life has crashed into ruins ...ND