You could do that. 40F is definitely not a temperature I would risk mine at, even if kept dry.

If you find that your adeniums lose their leaves (even can retain and be semi-dormant). I would move them out of the windows in an area of the home that stays at the temperatures that yo mention (60F - 65F).

Rick

I let mine live in the bathroom ... the moist air, I think helps. overflows go into the spare bedroom with grow lights, and I water occasionally... and the room is about 60

We keep our house about 70 and mine sits on a window sill with decent light. It usually drops a few leaves in protest, but then grows new branches where those leaves fell off. It doesn't grow much at that temperature and light level, but that's ok with me.