I have successfully overwinter them several times. I don't do a lot for them, except the sunny window, water well about once a week, and I usually cut them back. Yes, they drop leaves but put on new growth later.

However, even though they survive and grow healthily all the next summer, they rarely bloom again for me after that first summer- I don't know why

Thanks, Raee. I gave mine a trim, but will cut them back more. And hope for the best on rebloom! It's worth a try, since they don't show up in the stores here when I want them.