97 Eldo Head Gasket Questions

Hi I have a 97 eldo with 86000 miles, change the coolant and add the "pills" at regular maintenence intervals. My question is: that will they (head bolt threads in the block), ALL fail in time or will some of us be lucky?? I've heard from some mechanics, most would usually fail early on, when still in warranty or before 60-70k miles. How many out there have been lucky, racking up a lot of miles with no problem?? The reason I ask is that Warranty direct has an 80k, that means you can put 80k more miles on the car in 6-7 years for a $1300 warranty that covers up to $3300 on engine repairs and I believe $2500 on the drive train. Plus it covers cv joints, suspension , etc. Might sound like a wise investment, considering the cost of head gasket and thread repair.(?)