The potential had already weakened before the onset of the crisis, because productivity growth had slowed down. The crisis then made everything even worse, so today the euro area is on a much lower growth path. But monetary policy cannot change that. Monetary policy can only cushion the problem by, for example, making liquidity available and thereby helping to avoid a banking crisis.
This four year notice period should give market participants enough time to transition away from LIBOR, but the process will not be easy. Market participants that use LIBOR, including those in Australia, need to work on transitioning their contracts to alternative reference rates. This is a significant issue, since LIBOR is referenced in around $ trillion worth of contracts globally.