Airlock re-sanitization after minor blow-off

Good answers are already posted to answer the question. But one thing that isn't mentioned is the ways to avoid this from happening in the first place:

1. If you brew a 5 gallon batch have your primary fermenter have at least a 6.5 gallon capacity. Thereby allowing enough headspace so that active yeast growth and CO2 production will not blow out your airlock.
2. If you are brewing a high gravity beer or don't have a larger capacity carboy. Place a sterilized hose into the rubber stopper on the top of the carboy and place that into a container of sterilized liquid which is placed at a lower elevation relative to the stopper in the top of the carboy. Thereby allowing a sterile blow-off location saving you the trouble of a mess outside your carboy. Then after the active fermentation has finished affix a standard airlock.

It never hurts to be overly cautious with sterilization. That is why I always use sanitize on the mouth and top of the carboy and my hands before pulling an airlock if the beer is not finished out.

Introducing oxygen is nothing to be concerned about at this point. I'd say its safe to go ahead and clean it. Just make sure to sanitize it and anything else you touch that interfaces with the carboy, before you put it back. Some people recommend spraying sanitizer on the mouth of the carboy too.

Introducing oxygen is not a concern at all at this point. That's a bogeyman that's way exaggerated. You could probably leave it without problems, but I like to remove it and clean it when that happens to me.