The main problems you might have had (components getting fried by unexpected currents arcing through the liquid) probably won't have happened due to a) quickly having unplugged it and, b) being a low voltage/amperage device in the first place, and it not have particularly complicated electronics. (In fact you're more likely to have temporarily shorted the computer's own USB port(s), or at least caused its short-protection circuitry to kick in and deny the basic 5V supply for the duration, which should rectify in a modern device.)
If it hasn't yet dried then you want to make sure (including a droplet/meniscus of water within the optical component, which you should be able to check visually by gently shaking and looking for a 'spirit level'-like bubble moving around), but when equipment has dried the problem is usually the gunk left behind. e.g. coffee (especially very sweet coffee, colas, etc) that's not quickly drained out can leave behind a gunk that can cause you problems when you power on, or at least create mechanically inconvenient detritus when it fully dries and crumbles out to rattle around the rest of the device. (I've 'washed' laptop circuit-boards with various liquids from distilled water1 through to various 'smear free' glass cleaning liquids that evaporate once the visible coffee/etc stains... but it can be a delicate process involving cotton-buds rather than 'dunk and scrub and drain'...)
But if it was a quick dunk into water, you've examined it to make sure it's dry (including opening it up) then you're probably Ok by now. Plug it back in and if it doesn't work then you probably have ruined a component irreparably, despite what I said, so get a new mouse and try that. If that doesn't work, in the same USB port, then the protection circuits on the USB output board obviously didn't work, and you might just have to now permanently forget that USB slot (and possibly its companion, and find a different spare port or get a new USB interface module in the worst case scenario), but I'd say that the chances are against it going that far.
1 Has its own problems...