Now you mention it... my last cowplant died in winter too. I thought I had been too busy looking after the toddlers and hadn't fed it in time, but maybe it was too cold?
Anyway, as for the cowplant skeleton, it gives off a certain emotional aura, I think it's playful, could also be angry? But you'd need at least two cowplant skeletons near each other for it to appear. At least that's what I experienced, once, a long time ago when I set up a secret cowplant worshipping club and decorated their hangout with both living and dead cowplants.