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It sounds like the plant may have been in need of water, which I'm assuming you gave following the repotting of the plant. Plants in containers require more watering than those in the ground - once a day and twice daily in temps over 85 F. Here is more information on growing these plants which might help: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm

If temps fall below 50 F, the mandevilla plant will die. You should bring the plants indoors if this happens. That said, you may also wrap the planter in bubble wrap and cover the plants when harsher weather is expected. Keep in mind, however, that there is no guarantee this will work. Protection indoors is often best.

This article talks about mandevillas and overwintering in the house. https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-mandevilla-indoors.htm
Unless you need to keep the plant to a small size, you should probably let the new vines grow. If you put it outside for the summer, it certainly could flower.
Here is information on propagating these plants: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-propagation.htm

This article has some answers for you to explore: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/yellow-leaves-on-mandevilla.htm