If eternal inflation is correct, then the Big Bang is the origin of our pocket universe, but not the beginning of the whole Universe, which may have begun much earlier. The evidence for multiverses will be indirect at best, even with confirmation of inflation from Planck or other observations. In other words, eternal inflation could answer the question of what preceded the Big Bang, but still leave the question of ultimate origin out of reach.
Many cosmologists regard inflation as being the worst model we have, except for all the alternatives. Inflation's generic properties are pretty nice, thanks to its usefulness in solving difficult problems in cosmology, but the specifics are slippery. What caused inflation? How did it begin, and when did it end? If eternal inflation is correct, how many pocket universes could there be with similar properties to our own? Was there a Bigger Bang that started the multiverse going? Finally, since we're scientists and not philosophers, how can we tell all of these options apart: can we test them?
There is one possible alternative to inflation, which bypasses these questions and, along the way, resolves what came before the Big Bang. In Paul Steinhardt and Neil Turok’s cyclic universe model, the observable Universe resides in a higher-dimensional void. Coupled to our universe is a parallel shadow universe that we can’t directly observe, but is connected via gravity. The Big Bang was not the beginning, but a moment when the two “branes” (short for “membrane”) collided. The Universe in the cyclic model goes between periods when the branes are moving apart, accelerated expansion, and new Big Bangs when the branes re-collide. While each cycle would take about a trillion years to complete, the whole cosmos could be infinitely old, bypassing the philosophical problems with inflationary models.
The cyclic universe is not a popular model among working cosmologists, but at least it could be ruled out by experimental observations: if the gravitational-wave signature of inflation is found, then the cyclic model is dead. The cyclic model isn't complete: it doesn't explain how much dark energy there is in the Universe any more than standard cosmology does, for example. In other words, the cyclic model is not complete, so at present there's no physical evidence to distinguish it from inflationary models.
If you think all these options are fairly mind-bending, rest assured that professional scientists feel the same way. Since the observable Universe is currently accelerating with no sign of re-collapse even in the far future, why should there be a cosmos with a beginning but no similar ending? If inflation or the Big Bang erases information of what (if anything) came before, are we stuck debating over the number of angels dancing Gangnam Style on the head of a pin? Even if eternal inflation or the cyclic model is correct, it pushes the question of ultimate origin into the realm of untestability.
In another decade or century, the questions and the methods we use to answer these questions will most likely have evolved. But for now, it's unclear how we can possibly know what preceded the Big Bang.