I think there is a risk a lot of people would party more actually. (Knowing how much time you have allows you to plan better.)
Maybe at age 100 a person may decide to hit the gym, become a vegetarian, or do whatever.
Some people might do the opposite and let it rip at age 180 knowing they only have 20 years to live.
A lot would depend on what 200 would be like. If being 200 was equivalent to being 80 or 90 today then being a 100 would be equivalent to being 50.
If anything I think I would probably make the adjustment and add more years of risk taking, eating whatever I wanted, partying into the wee hours of the morning and so on.
Guarantees tend to encourage more risky behavior. A person who gets paid for sick leave is likely to take more days off than a person who does not get paid. A person living on a large trust fund is likely to splurge more often than someone living paycheck to paycheck. I think it's human nature that the more we have the more we waste.
What makes life precious is knowing it could end at any moment.
"Tomorrow is not promised to any man"
By not knowing when you might die you have to make the most of everyday.