Sorry to hear that. However, it may still be salvageable, if there are several growth nodes available. Growth nodes = places where branches fork from the stem or other branches. How many of those are there? Also, you can do a grafting-type of job - use medical or duct tape and slap the parts back together. Use stakes to support the top until the break heals.
Sorry, got side-tracked there. If you don't try to put it back together, the growth nodes are important. If you read this and you've already tossed the top part that broke off, you might try to recover it and try to mend it. I've done this with plants that had unripe pods on them and not only did the stem heal, but the pods also finished ripening.
But if you've decided otherwise, you can let the plant go dormant, as noted above. Preferably the plant should have at least 6 growth nodes - it's not necessarily an end-game if it has fewer, but at least 6 is ideal. Pull the plant out of the soil and trim the roots to about the same distance from the soil line that the top of the stem is. Pot it and water it. Put it in a cool place and get a fan on it. Don't give it a lot of light. Use the weight method (lift the pot and test for lightness) to determine when to water it.