I have a bit different look on what a lifetime guarantee means.My basic concept is the product is guaranteed to do the job it is supposed to for as long as the original purchaser owns the product.That may be the purchasers lifetiime.
Let me compare it to lifetime guarantee brake pads for a automobile.These are actually guarenteed for as long as the original purchaser owns the vehicle.This is usually not the lifetime of the owner but it is not the lifetime of the product either.
Say you bought some lifetime brake pads & in a year they were doing a poor job of stopping your car.You have a mechanic check them & find the brake pads are worn out.
Do you accept it if the manufacturer tells you well when the brake pads wear out that's the lifetime of the product?
I sure don't I owned one car for several years & had the pads warranteed 4 times before selling the car.
Software is no different to me & if it isn't upgraded permanently with the lifetime guarantee purchased with it.Then it no longer does the job it was purchase for & a full refund should be given.If upgrades are no longer available.You see the lifetime guarantee is part of what you purchase so it is not FREE.You have paid in advance for it.