One solution I saw somewhere here on HN the last time it came up was to carefully virtualize the existing systems so they have snapshots to restore from when th

One solution I saw somewhere here on HN the last time it came up was to carefully virtualize the existing systems so they have snapshots to restore from when things go wrong. That opens the possibility of moving the data to more modern systems with a translation layer between the 40 year old systems and the new systems that slowly replace them.