I have a vanilla game, and tried intentionally getting this to happen multiple times by stalling gym goers outside multiple gyms during freezing weather and blizzards
I can get one person to freeze by stalling them for hours after they turn blue, but there's no knock-on effect
The other Sims simply don't stay out in the cold long enough, usually they don't even turn blue after watching the reaper and then mourning for a little while.
I can imagine how it could happen. But it feels like the amount of time it takes Sims to freeze coupled with NPC free will makes it an unlikely hilariously freak occurrence.
Either way, it's simple to fix. Just get Sims to spin into warm clothes if they are going outside and it's cold, even in 'emergency' situations.
Regarding joggers: most of the joggers I've seen have been wearing their warm clothing rather than their athletic wear. I have seen one or two in athletic wear out and about with blue skin (perhaps the temperature changed after they spawned), but (again) it seems the amount of time it takes Sims to like actually freeze to death makes it unlikely to occur
Honestly, I'm kind of disappointed. I love myself some hilarious emergent chain reactions.