Probably not much... I would cut off the wilting parts and water the heck out of the rest of the plant. Awfully hard to keep pots watered in this hot weather... do you have drainage in the pot? If you feel like it, put some fertilizer in there-miracle grow type. Good luck!
First, check to see if your tomatoes are potbound--you didn't say how big your pots are. If there are not potbound, put a garbage bag that has pull ties around your pots--white, preferably. THEN, water heavily. Tomatoes LLLOOOOOVVVVEEE heat and water. When the soil is drying out too quickly, if you can keep the plant watered, your plants will do okay, and the bags will keep the water from totally evaporating. Tomatoes are really hardy, native plants.
HECK, I am planting cherry tomato seedlings that have been pot-bound for a month, and they're growing once they are in the garden. (Psst--I REALLY glad that nobody knows how much I abuse my 70-ish tomato plants!! )