U.S. shale gas will last a long time, and if they start getting low, the E.U. can simply start fracking for gas in the E.U.I think break energy deals between EU and Russia is a real big thing.
We can't see how much big now, because EU keeps consuming energy from another sources.
But when the other sources, like USA shale gas, will run out, then we'll see how big is and how different from any other measures.
Energy storage solutions will likely also get to a sufficiently effective point by then as well.
And that's without even taking into account that one can simply transition to Nuclear Power if all else fails.