That's the fear, in any case, among many European leaders and "Eurocrats" in Brussels.
The Lisbon Treaty's defeat in an Irish referendum on June 13 could push the European Union into a crisis that could dwarf anything the bloc has seen so far and put any further enlargement on indefinite hold.
The Irish result might well put into question the EU's entire drive for greater integration after its historic enlargements in 2004 and 2007, which contributed 12 new, mostly postcommunist members to the union.
The Lisbon Treaty was meant to replace the Nice Treaty, which was negotiated as a stop-gap measure in 2000 to prepare the bloc's institutions for enlargement.
The new treaty was already scuppered once in its earlier guise as the EU's "constitution" by referendum defeats in France and the Netherlands in 2005.
In its resuscitated and somewhat downscaled incarnation, it retained the basic goal of relaunching the EU's integration dynamic by providing for more majority voting and giving the bloc a president and a foreign minister for the first time.
The EU's leaders will get their first chance to collectively inspect the damage as soon as next week, when they meet for a summit on June 19-20.
The EU's upcoming French presidency, which starts on July 1 and runs until the end of 2008, will now need to focus on damage limitation.
Earlier this week, high-ranking French officials in Paris indicated in interviews with RFE/RL and other media that they will push ahead with the ratification process of the Lisbon Treaty, regardless of a "no" vote in Ireland.
"There is no 'Plan B,'" Jean-David Levitte, diplomatic adviser to President Nicolas Sarkozy, said. "I believe that what is important, is that the [ratification] process [which] is in train in all the countries of the European Union run its course, [which will involve] a parliamentary vote in all other countries in a manner which would enable us at the end of the process, during the French presidency, to assess where we are."
But Ireland's justice minister said after the result became clear that the EU is now in "uncharted waters."
Alexander Vondra, deputy prime minister of the Czech Republic, which assumes the EU presidency after France -- starting in January 2009 -- predicted in Paris earlier today that an Irish "no" vote would doom the Lisbon Treaty.
"If they vote no, I think legally it is pretty clear that each [EU member] country must ratify the treaty [before] it could enter into force," Vondra said.
Irish voters have rejected an EU treaty once before, in 2001, when they defeated the original Nice Treaty. Then, a declaration was added to the treaty affirming Ireland's policy of military neutrality, leading to its adoption in a second referendum.
Other countries have in the past negotiated similar ad hoc addenda to treaties. But that is unlikely to be good enough for Ireland, as France and the Netherlands won a wholesale renegotiation of the proposed EU constitution in 2005.
The rest of the EU, however, is unlikely to agree to a renegotiation, given the acrimony it is guaranteed to cause.
The EU now has to decide whether to content itself with the existing Nice Treaty or approve the Lisbon Treaty regardless of the Irish defeat. The latter option would necessarily involve the introduction of a degree of political isolation for Ireland, dangerously unprecedented until now in the bloc.
One of the biggest losers in the wake of the Irish referendum will be the EU's enlargement plans, insofar as they have existed. Pierre Moscovici, one of the leaders of the French opposition Socialist Party and a former Europe minister, made that point in Paris on June 9.
"I think that globally, an Irish 'no' would mean that the European Union would no longer be in a position to pursue further its policy of enlargement," Moscovici said. "For institutional reasons in the first place, because the Treaty of Nice -- I know this, because I was one its negotiators -- is designed for up to 28 [member states]. After that, we'll be in 'no man's land.'"
Of the current candidates, only Croatia would be guaranteed entry under existing rules.
That is liable to prove a particular blow for Ukraine.
France, which had for long years quashed the EU's eastern neighbors' accession hopes, has had a change of heart recently. French officials in Paris said the EU-Ukraine summit in Evian on September 9 could send "an important signal to the people of Ukraine."
Ukrainian diplomats have expressed hope this could take the form of an association treaty between Ukraine and the EU, paving the way for eventual candidate status. Moscovici said on June 9 that accession prospects could open up in "15-20 years." Kiyv's hand is now likely to have been fatally weakened.
Ireland's "no" could also further poison relations between the EU's new and old member states. The Lisbon Treaty was designed to be an essential counterpart for the bloc's historic expansion in 2004 and 2007 -- dubbed by many a "reunification of Europe" -- by allowing it to "deepen" again after a period of "widening."
But that is now in doubt.
Ironically, Ireland is one of the richest member states of the EU, largely as a result of decades of EU cash injections into its agriculture and infrastructure -- the prospect of which acted as a powerful magnet for the new member states in the East.