This definitely spells trouble for the EU. The Dutch will certainly vote no, I saw a poll indicating that a no-vote is possible even in Luxembourg. The conastitution is thus certainly dead. How on earth they're gonna rewrite it I don't know. The French wants it to be less liberal, the British wants it to be more liberal. I expect European integration to be on hold for a while now.
Probably not. We already got the Nice-treaty, which basically is a constitution, only a messier one, where the power structures are more clouded and the rights of the citizen less wellprotected.
Probably not be on-hold? If they couldn't get this through it's inlukely that the EU will convince the population of any further European integration. It can be done undemocratically, of course, but that would create a big back-lash. And the Nice-treaty is no constitution. It has no fundamental rights, purposes etc.