The Constitution was rejected by both France and the Netherlands at the last attempt. Both the prospective Presidents of France, Segolene Royal and Nicolas Sarkozy, are less enthusiastic about the European project than was Chirac. Equally, both would be extremely reluctant to be seen to be railroading through the Constitution without a further referendum. In its current form, and nothing has been suggested that would alter it, the Consitution is un-electable. From the left it looks like a facilitator of Turkish entry and even (somehow) a paean to liberal economics. To the right it looks like further enlargement of the role of the supra-national bodies, with a commensurate reduction in national sovereignty.
Referenda will have to be held in France and the Netherlands through sheer political expediency; in Denmark because that's how they always manage things like this; and in the UK because Blair promised one and Brown is unlikely to have the muscle or the balls to avoid one. It seems at least probable that the referendum result will be negative in at least three of these cases.
Completely ignoring the political/diplomatic reasons why the Constitution should never be accepted by the European Union; there is a cast-iron electoral reason why it cannot be. Calls for its re-introduction are fantasy.