After a no vote from one of the EU's major founding members, the EU is now faced with the painstaking question: Does it make sense to go on? This is especially relevant for the public in in the countries where a referendum is planned.
Legally speaking the situation is clear and is set out in Declaration 30 on the ratification of the Constitution:
"The Conference notes that if, two years after the signature of the Treaty establishing a Constitution for Europe, four fifths of the Member States have ratified it and one or more Member States have encountered difficulties in proceeding with ratification, the matter will be referred to the European Council."
There must, however, also be an expression of clear political will if the momentum is to be kept up. Otherwise abstentions may mark future referenda, most importantly in the Netherlands that will vote on 1 June.