A latest take on Boris's negotiating stance with the EU (in the Times recently), is that if he agrees a deal now, the deal will swiftly be seen as being crap by the general public, with all of the long touted disadvantages of such a hard brexit (that Boris has always said he has wanted) being seen for what they are. So do a deal and be damned. Or....
Don't do a deal and impose even greater hardship on the UK, with the massive fallout out of a no deal hitting business and employment hard, but be able to contrive that it was all the EU's fault and somehow not be damned.... if enough people believe him.
There's a big chance he'll opt for the latter then