A short extension seems more likely than a long one but there is also the responsibility of the signatories of the GFA to uphold it whether there is a deal or not. This has to be resolved whatever happens. Possibly some kind of border in the Irish Sea? There has to be an answer eventually.
I read that as as a short extension to ratify the deal as it is now... otherwise a long extension
Basically if MV3 passes ok go with a short extension
If it fails (and it probably will) then the EU say go on 29th or start a new negotiation based on new redlines, or with a new government, or show us you are having a referendum
Which will probably involve MV4 on wed 27th about 40 hours before we leave...
basically may pushing it to the last moment of my deal or an extension... but still with no deal as the default and the ERG etc trying to make sure that happens
My gut feel is that if labour moves the official position to Mays deal subject to a referendum there may be the votes to get that past... but that she would rather roll the dice on a general election than let that happen and so would corbyn
Extension to 30th June would allow for a GE I think (though clearly not much time for a new government to do anything)
Id say 35% we have a GE (most probably a hung parliament and no further forwards)
30% we have a 2nd referendum (close to 50-50 and nothing really solved)
25% may gets her deal through and we move on to fighting about an actual trade deal that simply wont be close to being completed in the timeframe and therefore nothing much changes
10% we get no deal in which case we panic and start trying to do an actual trade deal ASAP and nothing much changes
to be honest I think its going to drag on for a long time whatever way they fudge something