There's two options, hire overseas at a lower labor cost (lower currency/lower minimum wage), or lower the minimum wage or currency of your own economy. If the labour costs of the rest of the world increase as their economy develops, it will make sense to employ locally again.
So subsistence wage moves from overseas, back local again... and why pay more than the subsistence wage if there's no government to compel you to do so?
Edit: Keep in mind, the US is a western democracy, and the largest economy, but has plenty of people living on subsistence wages.
> could just as easily be a rise in extreme protectionist tariffs to discourage offshoring thereby re-widening the gap
Protectionism may not re-widen the gap. Many populations starve because all their arable land is used for overseas exports.
Nah, it's too politically unsafe to hire cheap in your own backyard and there'll always be country-level wage gaps on the bottom end, I'm just glad they're (slowly) reducing. No need attempting to run the simulation to a hypothetical end because there either is no end or it's unpredictable (could just as easily be a rise in extreme protectionist tariffs to discourage offshoring thereby re-widening the gap).