One strategy open to Johnson is to proceed with the Bill and simply to live (for the moment) with a Christmas tree of amendments (such as customs union/requirement to seek transition extension) that do not stop ratification or require re-negotiation with the EU.
(That category wouldn’t include a 2nd referendum amendment - which would stop ratification: but it is unlikely that there are the votes for that.)
The fact is that, after an election where he gets a majority (and that must be his medium term aim), he can simply pass new legislation to strip the Christmas tree of its unwanted decorations. And if he doesn’t get a majority we are in soft Brexit/CU territory anyway.
