This is currently being mooted around the capitals of Europe.
Reuters UK Germany says EU may still pursue EU Treaty
It's a fascinating legal and political question. I'd have thought not, but I think at a minimum there would need to be agreement from the Commission, unanimous agreement from the Council (including Ireland) and the parliament not to mention the ECJ' at least tacit agreement (maybe someone should ask them).
In practice I think it's a lot harder, you could end up with "Lisbon" members and "non-Lisbon" members of the EU. It's quite difficult to determine how you can be in the EU and not be affected by Lisbon if it enters into legal force. Proposals to end the rotating Presidency can't be adopted in part. Of course, if there's only one "non-Lisbon" member....
For this exercise to have any legs at all the Associate membership option ("non-Lisbon" membership) might be worked up into something attractive and non-punitive (keepng your MEP's and Commissioner etc). It would become an EU membership status for a member state that had not ratified a Treaty provision and under it the country concerned would retain their legal position as to internal law (and therefore any cases before the ECJ) as per the last treaty that had been ratified and in force.
And of course the Irish government would have to be willing participants.
Is this realistic? Is it pure fantasy? Denial?
All eyes now on Sarkozy and Merkel for the next chapter in what promises to be a long running saga.