Overlooked Scenarios
1. Niche software (Poison Control Center case recording/realtime monitoring software, Industrial Frobbitz Control Software) written by a garret-resident Wizard, who is too busy fixing bugs and adding new features to migrate to a newer DB (Said Wizard just finished migrating from Btrieve to MS SQL of some version, a few years [decades?] ago, for Heaven's sake!).
1a. Wizard dies in their garret, there was no designated Successor Wizard, and anyway, the source is kept encrypted on DECtapes. Nobody living knows the password. And, it's not "xyzzy".
1b. Wizard closes business, sells all worldly goods, and moves to a California treehouse amongst the redwoods to contemplate the Meaning of Life.
1c.Wizard sells business to a Giant, Acquistional Software Monolith ("GASM"), which then forms a new business unit to sell, enhance, and support the software. This business unit is located in the basement boiler room, and staffed with a couple of Eager Trainees ("ETs") who wonder what these spools of brown stuff sitting on their desks are and what they ought to do with them.
1d. Software is acquired by GASM, as in 1c, above. GASM then shutters new business unit, "to align with our core values and increase operational efficiencies." Suggested upgrade path is a purchase of, and data migration to, a different product owned and supported by GASM.
That product is an add-in for SAP S/4 HANA.