Well, put it this way. I actually took some of my tomato seedlings, when they were barely showing their true leaves, and cut the stem halfway up and just replanted a bare stem with no roots at all (they were leggy).
Now, about a month later, they are all growing fine. They are about a few weeks behind the others (sine a whole new root system had to be established from the stem), but I've no doubt that they will catch up.
Even if you get a few roots still attached to yours, they will surely do great; those tomatoes are pretty tough.
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