What happens to a cable exposed to alcohol?

It should be fine. The worst that will happen is that your computer will explode. Okay, kidding. It’ll be fine.

The alcohol evaporated way before it got a chance to do damage.
Besides, USB cables carry low voltages, it will be safe to handle even if it decomposes.
If you see the insulation decomposing then stop using the cable as your data signals could start getting compromised.

I just checked it out. No visible damage. Which is good, right?

Probably it’s completely fine. Check it again in a couple weeks to see if there has been any distortion in appearance where it was exposed &/or before you use it next.
If there seems to be anything wrong with it at all then just use another one. They’re cheap and you might already have one from another gizmo. Just assure that the two ends have the same kinds of connectors as the suspect one.

Welcome to Fluther.

If it’s dry, then it’s fine.

Just don’t let it drive.

I wipe down cables at work (hospital OR) with alcohol disinfectent all the time and have never had any problems.