K.P.
Oh, I hear ya! My first-born weaned in a day at 13 m/o -- went from nursing before and after naptime and bedtime to nothing, nada, zip, zilch, zero. *sniff*sniff*
It may just be a temporary nursing strike (perhaps due to a cold or teething; in my case it was a permanent strike because I was pregnant and the milk changed), so it might be a good idea to pump in case he changes his mind. Even if he doesn't, you can always give him breastmilk in a cup or bottle, rather than switching to formula (which is inferior to breastmilk) or to cow's milk (which is for calves, not humans). He'll still be getting the health benefits of breastmilk and getting milk that is perfectly made for him, even if he isn't nursing.
Babies are good at getting what they need, so I wouldn't sweat it if he doesn't drink too much. Offer him to drink as much as he wants, but he'll stop when he doesn't need more. My two children are quite different when it comes to drinking -- my older son is like me and drinks lots of water all day long, while my younger son is like my husband and drinks very little. With your son eating food and drinking some water, he may not need much breastmilk, as far as for hydration (particularly if the food he's eating is very moist). Still, I would pump and give it to him to drink if he gets thirsty, whether he nurses or not.