I do not believe Iran will be able to prolong any further existing biting sanctions. So it is all right for USA and Western Powers to return from negotiations without any agreement.
Fundamentally, Iran stopping construction of nuclear plants which can produce nuke material is a must. Arak plant construction must stop, that is essential. IAEA inspections are must and there cannot be any ambiguity in terms of Iran not being able to pursue weapons grade nuclear material. All these things are non-negotiable and hence Sec. Kerry is right to claim that 'no deal is better than a bad deal'.
Iranian President Rouhani will find it harder eventually to continue his credibility without delivering a pact with Western powers since that is a necessary condition for normalizing lives of common Iranians. So overall - hang on, Iranian Ayatollahs will come to terms with restricting their nuke bomb making activities. USA and Western Powers simply have to hold tight. Else in next six months, Israeli attach on Arak and other Iranian nuke sites cannot be ruled out. That will not be any easy for the world economy.