Tell me if I've missed any:
(some are niche)
Labour govt (either majority or relying on other parties) gets referendum between Johnson's deal/tweaked withdrawal agreement & remain.
Requires immediate A50 extension to middle of next year. Remains wins referendum, A50 revoked (nightmare for EU budget?)
Same as above but remain doesn't win the referendum. Result most likely soft Brexit - Single Market/CU.
UK leaves the EU next summer.
Labour led govt, relying on 2nd ref/remain parties to get working majority. But Labour backbenchers who are against 2nd ref retain their seats and we have, Theresa May style, a frontbench that can't carry enough backbench MPs on Brexit
Conservative minority that rely on either DUP or Brexit Party - where price of confidence is the junking of all or parts of this withdrawal agreement.
January is a nightmare.
Very slim majority for conservatives. WAB goes through in January but on next phase talks Johnson has no room for manoeuvre and has to keep all (often competing) parts of the party happy.
Transition extension in June is big test
Big conservative majority - WAB sails through and Johnson has potential to upset parts of his party on the future relationship.
(e.g. Extension less contentious, fish less of a difficult decision - particularly if scottish coastal seats are lost)