I seriously doubt they'll be surprised by this. McDonnell and Milne may be utter scum, but (unlike Corbyn) they're not stupid. They'll have a contingency plan, so I'll be interested to see what their next move is.
The thing is, there really isn't anyone of substance among these seven and their 'leader' Umunna's a pretty boy, but as thick as a brick. They'll need others to jump in order for them not to be marginalised, isolated and destroyed.