Remember, at the political level, if France (and Germany) put up the proverbial finger to the EU then it is all over. Very unlikely, despite current difficulties over the euro and Greece etc.
I don't think it is so clear cut.
The only EASA output so far to make law is the Basic Regulation. This is so vague it is worthless. For example is says the EU has authority over foreign regs. Well, what else could it say? That the EU has
no authority over foreign regs? Nobody would have voted for such an abdication of sovereignity, so everybody voted for the BR. It's an old political trick.
And nobody has a real issue with the BR. It merely states (vaguely or otherwise) the infinitely long established present position which is that if the CAA rep at LHR sees a Thai 747 whose engine is about to come off, they can ground it and it will stay grounded until somebody comes along and tightens up the engine bolts
It is all the stuff in the EASA pipeline that is the problem. None of it is EU law yet, and all of it is subject to " a good lunch and bottles of wine, " etc.
It is the anti foreign reg provisions in the later stuff, not law yet, which have been dishonestly justified by EASA as being required by the BR (which is already law) which are subject to change if somebody makes a really strong stand.
It's like Bob Geldof going on stage and saying "tonight we will abolish poverty" and after everybody cheers (and everybody with more than 2 braincells knowing it is just plain daft) BG then sends the military to take over Africa, etc
That's essentially what EASA has done - a fairly basic political trick.
If say France sticks a finger up to the EU at
this stage on the IR, the EU will have to modify the stuff in the pipeline, otherwise (as you say) the EU game is over. It's quite a gamble, but France will always win that one because it is not worth fighting over in Brussels. Not when Greece is about to bring the whole edifice down anyway.