Most plants that live happily where it freezes every winter need that freeze cycle to flower
the next year. That's why they don't grow apples in Florida - without the cold winters they won't flower
and set fruit. My guess is that you can keep your mum indoors for many years as a foliage plant, but that it will not flower
next fall or flower
weakly and not at all the following fall. But, I'm not 100% sure. Generally, I'm of the 'get another one so you have a control and an experiment plant, try it and see what happens' kind of person. You just have to let us know if the indoor one flowers
next fall, please.