This is a freak kind of thing. While those of who've been around long enough have seen a few cracked plates, almost exclusively outer, it's not a common thing.

So, other than standard care in maintenance and lubrication, nothing special is called for. Odds are you won't see another cracked in your lifetime, and your concern will be about wear, not breakage.

Though we can't know the timeline you might conduct an experiment with this chain before chucking it. I'd love to know because inner plate failure is so rare that there's not much known about how much load it can manage.

Break a plate, or push a rivet through slightly, so it's not connected at that place. Add some load by either yanking on it, or putting it back on the bike with the broken link on the upper loop, and stepping on a pedal.

We know that a broken outer plate the load is so imbalanced that it immediately pulls apart. However inner plates are close to the center line, so the bending force is much less, which explains how survived that long. (or it might not)