Johnson knows how fucked we'll be without a trade deal of some kind.
Cummings wanted to go full steam ahead and assume the other side would blink first (a tactic he's espoused in the past)
Johnson has realised how fucked he'd be if we have food riots.
So Cummings is out and over the next week we'll magically find ourselves with a deal.
One that sucks compared to membership of the EU, but at least some kind of a deal.
Original post on Dreamwidth - there are comments there.