Can't say for sure. I know the marathon runner challenge can help but not sure by what percentage. There is a percentage chance they will roll death each day after their bars are full but I have no idea what that is. For all I know, lifespan might be taken into account as well. I am currently playing a 50 something day life span and I would be very concerned if my elders lived that many days over but when I play longer lifespans I often see sims quite a bit over the full bar.