[jfengel]

Pretty close.

The wave function is still symmetric, but it takes on a bimodal distribution, with very little overlap. For any given event, it will be affected only by the half of the distribution that it's in. The other half has basically zero effect. The further time evolves, that effect becomes even smaller -- as in, the odds of an experiment demonstrating it quickly go towards 1 in 10^googol^googol.

You can round that down to exactly zero and call it "collapse". Or you can keep thinking about the entirety of the wave function, and call it a "multiverse". That rounding is technically invalid, but it simplifies the conceptualization (and the math) to a massive, massive degree without affecting the outcome in any pragmatically measurable way.

(One more caveat: "symmetry" implies we're talking about a wave function with a 50-50 superposition. That's not a requirement, but it simplifies an already complex explanation.)