Did your flowering vinca look like this after a chilly night?
No, it’s not dying.
Flowering Vinca is one of several plants that so prefer warm (even hot) weather that chilly nights, even when temperatures remain above freezing, cause them to wilt. Other plants that show this cold-induced wilting are morning glory and sweet potato vine, angelonia, basil, and caladium. Most of these plants originate in tropical areas that rarely see temperatures dip into the 40s (F).
What's happening is that despite adequate water in the soil, (in the picture you can see the soil is quite dark and moist) the cold roots of the plant cannot supply water to the more active top growth. You usually see recovery follow the sun as it warms the soil. Rarely, the wilt is severe enough to cause some permanent leaf damage. Caladium, morning glory and basil are particularly prone to damage and leaf burn from cold nights. (Caladium can lose all their leaves and retreat completely underground until the weather warms up.)
Sometimes the warmer & sunnier it had been the previous day, the worse the reaction will be. It is important that you do NOT water plants that are wilting like this, as they are more susceptible to root diseases when nights (and therefore soil temperatures) are still cool.
In most cases, your plants will recover completely, or with minimal long-term damage.