For MEB, forever.
John Maynard Keynes remains an important economist to understand, as do however Hayek, Friedman, and even the less-well known critic of Keynes, Von Mises.
Nonetheless, the current economic state is proof that if Keynes is useful for certain types of economic analysis, his rejection of Schumpeter's insistence that the long run Classical identities mattered more than Keynes' analysis allowed, "In the long run we are all dead," went far too far.
It was predictable that given the long run budget constraint that applies to all entitites, governments too, that the use of stimuli in the Keynesian fashion of what has become its own orthodoxy would not have as much effect as desired, if the Classical opposite of "Ricardian Equivalence" now embedded in Rational Expectations theory and policy prescription goes too far too, due to the "non-conservative field properties" of human activity.
The value conservation assumption at the heart of Classical theory, now in rational expectations equivalence to General Equilibrium Theory of microeconomics goes too far, which means government has some role, if one that decreases depending on the state of the long run budget constraint.
Since the long run constraint of an aging population is telescoping into the present, in terms of Baby Boom generation retirement, the long run contraint has to be taken very seriously, especially by Keynesians, in order to preserve on a prioritized basis those governmental functions they may be correct offer the best hopes for increasing economic output, Research and Development because of externalities due to imperfect enforcement of intellectual property rights.
Zandi would have the right idea in this regard, as to the need to scale back the macro-shock of raising taxes from the Bush rates while doing the sequester, but only by showing credibility as to a long run budget, which balances the truths of Keynes in the short run and the increasing importance of the Classical view of the long run.