"Mr Reinfeldt said talks have been held about what to do if there is a No vote, particularly on how to comply with the Nice treaty provision that mandates an immediate reduction in size of the next European Commission.
Mr Reinfeldt said a “26 plus one option” was probably the best solution, whereby 26 states retain their commissioner and the 27th state is offered the post of high representative for foreign affairs instead. This would give all 27 countries a top EU job, while complying with the legal condition for an EU executive of less than 27 members, which is stipulated in the Nice treaty."
However, he also said that the time could come when the Commission needs to be reduced:
"But he said was still a question about the efficiency of having up to 30 commissioners in an EU executive if further enlargement occurred. “We might in the future get back to this discussion. What if we keep on enlarging? But for now it’s very important that this was a call from the Irish people and we have met it. I know this was a factor in the Irish referendum.”"
It's an issue that I've argued we can't duck forever, but it's clear that for the foreseeable future there will be attempts to keep the Commission as big as possible. That's not to say that this is a definite Plan B - Reinfeldt has only described it as an "option", and there's no written political commitment from the entire Council, in comparison with the Lisbon Treaty guarantees. Since the No side rejects the validity or trustworthiness of these guarantees, it's hard to see how they could (honestly) capitalise on this statement as a "guarantee" for the No side. There are still some states in favour of slimming down the Commission (particularly Germany), and the original Lisbon system of a member state having a Commissioner for 10 out of every 15 years could be revived in some form in the case of a No vote.
Still, a No vote represents political uncertainty when it comes to European constitutional reform. Even though amendments to the Treaties must be unanimously passed, the fact remains that the member states are still sovereign states who can decide to carry on in a different direction if need be. The idea of a multi-speed or two-tier Europe isn't a fanciful idea, especially given the range of opt-outs and opt-ins there are already. Since the last 9 years have been focused on achieving a common agreement; if Lisbon is rejected without any clear path or solution for the way forward (i.e. do we know what we would want changed, and is it possible politically to change it?), then a multi-speed Europe can't be ruled out.