I saw this happen before, too (well, not with parties, events or travel, but in the comfort of the sim's home!), and two sims have died so far (NPCs) in my 100 baby challenge save because of cold weather.
Luckily none of my played sims knew them or witnessed their death, but the camera had switched over to them freezing to death. The first one was a MCC-generated sim named Matilda House, and she was just sitting on a bench the last time I saw her before she died.
The second one was a Maxis-made sim, Nancy Landgraab, and she was just jogging. Honestly, I agree it's the townies' faults here when they don't wear the proper clothes.
Then a creepy thing happened in my game, and I'm not sure if it's related to this, but then they somehow revived with me having ABSOLUTELY nothing to do with it. At first, I saw Nancy Landgraab at a bar and she tried to chat with my matriarch.
Then I saw Matilda House casually walking down the street. I checked them using MCC Cheats, and they were homeless, apparently, and had no spouse. And I'm pretty sure they lived in a house and had a spouse (I went to Manage Worlds to look at all the NPCs that lived in houses).
Honestly, I don't know what happened. It's not a big issue for me, but really, really odd (especially with them reviving).
