I guess it would come down to a combination of the companies risk tolerance and the cost of the worst case scenario. Eventually the system is going to blow w/ou

I guess it would come down to a combination of the companies risk tolerance and the cost of the worst case scenario. Eventually the system is going to blow w/out possibility of repair, now you have the expenses of downtime + replacement. So one argument in favor of replacing "prematurely" is to prevent just that. Like how you might sell a car for higher towards the end of its life instead of waiting until it's EOL, since now you get less money for the car and suddenly need to buy a new one. Granted, a replacement system could be worse than the original.