My uncle built a system for a large warehouse wholesaler in a minor European country in the 1980's and devoted the last 35 years of his career to maintaining it past retirement age. Over the years technology improved and the front end got more sophisticated but underneath it got more and more janky. They tried to move to a system based on SAP but the whiz kids they hired to set it up made a dogs dinner and in the end they were still using his system. In the end they found someone to hand it off to who shadowed him for 2 years to learn its ins and outs. It was supposed to be phased out in 2023 about 5 years after he retired but its still running and every once in a blue moon he goes in for an afternoon to troubleshoot something particularly vexxing. Last time he went in the guy who maintains it told him it will be at least a decade before its retired at the rate things are going there. My uncle is 76 and has survived cancer. Its likely this system will outlive him and if it suffers any serious errors it may simply not work all of a sudden.