My rear wheel has 24 spokes (700c rim, running 25 mm tires, semi-aero rims, Bontrager SSR). I noticed the other day that it was out of true by like 4 or 5 mm, easily; I think it was from when I hit a lip in a road while negotiating a turn (must have been a good 2" tall--the kind of lip left when they tear up some pavement to repave--but are not paving the side road). I quickly located the loose spoke, and it must have taken probably at least 5 turns to bring it back in. I did tweak a few other spokes--I barely know what I'm doing here--but those took like quarter turns. Now it's like a mm out of true, more than good enough for me. [I couldn't tell it was that out of true while biking.]

All the spokes are relatively the same tension now (but I don't have a tension meter, and I'm totally tone deaf), and "feel" tight.

What does this bode for the future? I'm thinking that spoke got stretched, and it will probably loosen up again on the next hard hit (or just slowly over time). But that's just the nature of the wheel, and it'll do that until I either replace the wheel or at least the spokes, right?

There's no such thing as a stretched spoke, and you handled the wheel truing nicely.
There will be no fiery explosion.

Ride the sucker.

Oh, I plan to! I figured, worst case, it'll just go out of true, and I'll have a great excuse to upgrade.

Thanks for the confirmation.

The above assumes that the sudden load at the bump compressed the rim elastically enough to make the one spoke lose tension (and with it friction against the nipple threads) momentarily. Residual wind-up improperly left in the spoke during building allowed the spoke to unwind in the nipple, loosening it. In this case, before you starting re-tightening you might have seen a vertical "hop" in the wheel, as well as out-of-true-ness. (You notice the hop more, the fewer spokes there are.) Both would be corrected by tightening that one spoke back to the way it was before. If so, congratulations on your diagnosis and repair.

Sometimes, though, when you hit the mother of all bumps, you dent the rim permanently inwards (toward the hub.) This loosens one spoke because that spoke hole is now a couple of millimetres closer to the hub. The nipple might not have loosened on the spoke at all, but it will take several turns more to bring it tight again, and you may run out of thread. Rims dented this way are often not out of true despite the one loose spoke, a tell-tale sign. If you can see a "dip" at the brake shoes every time the wheel goes around, it needs more than just a tightened spoke. Such a wheel is safe to ride (unless the brake shoe hits the tire at the dip or if the rim sidewalls are splayed out enough at the dent to catch the brake shoes and make braking grabby) but the dent should really be hammered out (or the rim replaced) to make a nice smooth-riding wheel.

But it sounds like you had it right.

2" lip isn't that bad at 15 mph with a 150lbs rider. Course the average 24h stock wheel is not very strong. I'd inspect the rim for any "flat spot" and crack if you have to crank the spoke by 5 turns.

It is possible to correct a 5mm wobble by turning one spoke 5x, but this will place a lot of stress on that spoke. Unless the rim is defective, a good wheel builder should be able to correct this problem by moving a few spokes less than one turn.

I didn't see any crack, but I didn't think to look too closely--will look again. No flat spot that I could see, but it's a semi-aero wheel, I'd think it'd be pretty hard to flat spot one of those. As for the stress on that spoke (or others), they're all about the same, at least as well as I can tell with my bare hands.

Pluck the spokes like a harp or guitar, the tones should be about the same pitch for spokes on the same side. If the rim has eyelets, check to see if the affected one is loose. If I remember correctly, Bontrager SSR wheel were prone to issues with eyelets.

If it is a Bont wheel with the spokes spaced with groups of two it will be failing.
Not particularly from what you did either.
Most of the people I ride with that have those have developed cracks in the rims near the spoke holes and have had them replaced only to have the replacement crack also.
If they are the newer ones with the spokes spead evenly around the rim you are probably OK.

No, they are paired together, not evenly spaced. That's a bummer, as I like the look of these rims. I'll just keep riding it, at least until it goes out of true again. I'll look for cracks tonight, but I'll see how they hold up before rushing to replace. I'm not a powerful rider, so perhaps I can eek out another summer on them w/o worries.