It depends on how healthy the root system is. 2 years ago a rabbit ate the tops off all my seedlings. They were nothing more than a stem sticking out of the ground but all came back.

I had some deer come down and eat the tops off 8 tomatoes and also they ate 4 young cucumber plants. Im pretty sure it was deer by the observation of their footprints in the soft post/rain soil. Some of the tomatoes had a leaf or two left, some were just a stem, miraculously all of them came back to life with new growths.
I been spraying a homemade deer repellent mist on the plants after that. I mixed 2 beaten eggs with 2 cups of milk, a couple gloves of garlic, a couple teaspoons of various hot sauces, a tablespoon of dish soap. I blended all that stuff in a food proccessor, then i squeezed it through a nylon sock and then diluted it with a few more cups of water for application in a spray bottle. It seems to be working so far ;)