You know what ?

Germans, French, Belgians could say yes or no to the EU constitution, it is all the same. The only thing that counts is whether the British say yes and they won't.

The problem is that the German and the French (and Belgian with a debt of 160% of the GDP) would shoot in their own foot if they say no, but they only would have to rewrite a constitution. Spain, Italy and EasternEurope countries have a geographic problem if they don't comply with those countries. Another way to solve their position problem is to turn their relation to Russia which they will never do.
However, that said, there may be a winning case for them if UK quits the EU and another Union is made apart from France and Germany under the cover of the US and UK lead through the NATO with Turkey joining and probably Switzerland. The great winner would be UK, especially if they join the Alena. Then France, Germany may have to build ties with Russia and Northern Africa, especially Marrocco. The later Union will be very fragile, especially because politically those 4 groups (Northern Africa would be very populated) are equal. This group of 4 entities may even ally India when the rest of Europe may prefer China (because China would prefer them).
The latter will happen if UK votes NO for the European constitution.
To counter that Germany may consider a referendum to obtain a NO and have to change the constitution to look appealing to the UK (France has already done that job earlier for the Euro and nearly missed to answer what the voters were supposed to).
People may be wondering why I presume that second weird European group. In fact considering France and Germany will be left alone, this Union will be the best they could have and mandatory for them to survive even as countries. on the contrary, if UK quits the EU and the US is willing to support a NATO based Union, which they already do, it is obvious those countries out of Germany France and Belgium which are unfitted countries for World competition would be relieved from the support they will have to bring to those socialist economies. There is a big unsatifaction among the newcomers to have France Germany and Belgium supporting socialism and Soviet style administration. This is even deeper considering that the opinions in those countries are basically hostile to the newcommers and Soviet Union mourners.
Another case applies to Spain which economy is usefull to the rest of Europe and may not suffer any export declining but will suffer tax and currency support for French and German fading economy. The only special case is Italy which may suffer being in any of those smaller Unions.
That said analyst already estimate UK GDP being on par with that of Germany and France together in 2025.

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From SR