"Mitigated" No deal: so no WA, no transition period, but rather a bunch of hastily arranged temporary arrangements & agreements that will allow the airplanes to keep flying, medicines arriving & goods lorries to only have 2 minute delays each. Bitter wrangling about UK paying for long-standing commitments until the £39bn is finally coughed up after all.
Also military deployed to manage logistics of all the huge backlogs of lorries delayed at ports. Might be some kind of facilitated movement of lots (more than now) lorries thru other ports that have capacity like Harwich, folkestone. Realistic prospect of ROI pursuing UK govt for GFA violations thru whatever recourse ROI has, about hard border in Ireland.
I predicted all this > 1 yr ago as the most likely outcome, not happy it seems to be coming true.
If no FTA in place by late 2021 then Nissan & other manuf'rs will en masse depart/decline to upgrade/not future invest.
2nd most likely situation: revocation of A50 in mid March with promises to come up with a full plan before invoking A50 again. This will mean nasty possibly somewhat violent/anti-social public protests. And no real Brexit for at least 4 yrs. That would happen after asking about A50 extension period, but EU will point at MEP elections due in May, & revoking A50 will be seen as lesser evil.