You can root the part that broke off in soil. The problem is, you'll probably want to shade it for a few days, or the sun might kill it. Just plant the cutting in the soil, water it, and shade it. After a few days, if it's still alive, it should be fine.
I've done this before for at least one tomato plant that a cutworm or something like one severed, granted I didn't need to shade it since the area was already partially shaded. The knowledge of sun killing new cuttings (and some transplants) comes from experience and observations with cuttings and transplants.
Humidity domes can help outdoor cuttings, if it's not too hot (think less than 80° F.) but it's not really necessary for tomatoes here.
Giving the plant a little extra potassium (e.g. potassium sulfate) should help the plant, too (to absorb water and other stuff), but again, it's not strictly necessary.
As for the other part in the soil, it may or may not grow again. If you could put that indoors very close to a 22+ watt fluorescent bulb, it might grow new shoots.