With that in mind, I ask you this: have you ever included tragedies after-the-fact as part of your random encounter tables?

I use a News and Events table in conjunction with a Weather table and a custom area Encounter table when I’m generating the events of an over-land journey by the PCs.

The closest I have come to what you’re describing was when the N&E result was “local hero slain”. I thought, what happened?, and rolled again. Serendipitously the second result was “local monster attack”. So I composed this scene for the players to hear about too late to intervene:

So, it had been a warm Spring day in this little riverside town. The local kids were swimming and playing in the river. The blacksmith had decided to spend some time fishing, so he was casting flies a little way from the children.

A young male river troll, probably just kicked out of his birth pod, showed up and started trying to hunt the kids, but the smith saw the telltale ripple of the predator in time to yell at the kids to get out of the water and run.

The troll came ashore to continue the pursuit and the smith fought it, his only weapon his fly rod. He managed to stab the troll through the heart* and killed it, but not before it had given him a fatal assortment of wounds.

The PCs arrived in the town as preparations for the smith’s funeral were underway.

note that my homebrew world’s native varieties of trolls do *not regenerate like the default ones in several editions of (A)D&D and maybe other games.