They simply replace it every 10-15 years with a new, as by then you would be getting into the end of the bathtub curve for reliability.
As to those PM3 flatpacks, they are aerospace rated devices, and very reliable. They survive being launched on unmanned missions and even are used in missiles. They just use a drop of thermosetting epoxy to glue them to the board during assembly, so the solder joints do not have to handle stress. Leak testing during manufacture is 100%. They are very reliable, much more than overmoulded DIP devices. Only drawback is that the package cost is so much more than the chip inside, even if you are only making one wafer of chips to package in there. Just like the old Intel ceramic packaged processors, where the cheapest part was the die inside.