I assume it wouldn't be too different from how it works now. On phones without a home button, you press volume up, volume down and then hold down the side button. This forces a reset even if iOS completely froze/crashed. Now this same low-level interrupt (or whatever is actually happening, I'm not sure) works with solid state buttons instead. I don't see the problem. It's not like the current side button physically cuts the power if you hold it down for 5 seconds, there is some low-level firmware running that listens for that key combo and then resets the SoC.
Come on, I know many people in the Fediverse dislike Apple, but do you actually think they'd not think about that..? This would blow in the press up a few weeks after launch and Apple surely wouldn't want that.
I feel like this might be one of those things where people are like "oh this is bad" but then >99.9% of the people actually using it are completely fine with it and all the issues people talked about beforehand like resetting when the OS froze will be non-issues because it'll work just like it did before.