If you don't think he's eating enough, what kind of solids are you offering? Are you giving him protein and fats to fill up his tummy so that he can sleep better? If he has never been big on eating meat, this could be a good chance to get him interested. And lots of water if he won't drink milk - you could even add a splash of juice to the water to encourage him to drink it if he's dehydrated, though that can exacerbate diarrhea. If he's getting most of his food from solids, he will probably need three solid meals and 2-3 snacks at this point. Yogurt could be another good food for him if he's not drinking any milk. Mine likes plain yogurt with a little spreadable fruit mixed in.
Definitely pump if you don't think you're ready to wean yet, but be careful - if you overdo it, you may end up engorged, especially if he doesn't return to the breast after all.
My baby weaned himself at 11.5 months because I was pregnant and had no milk supply anymore, so I don't have any advice for getting him interested again. I hope it works out, though!