> we can call a technology dead once no new business is built on it
You don’t suppose any bank - or other large financial institution - might have standardised on Cobol for their core business flows/processes? In which case a new business-unit or “internal startup” team (e.g. a new category of insurance product) might very-well have some part written in Cobol so it integrates with the rest of the bank - or at very-least might be built-on-top of the org’s existing Cobol-running infrastructure (i.e. Not written in Cobol, but still runs on Z/OS because there’s no budget for buying new commodity x86 racks and the people to manage and run them).
I was under the impression that banks with core COBOL processes all had an intermediate layer in Java/C# to deal with these kind of integration.
We saw exactly the case of a new business unit being created, and like most other units it wouldn't get direct access to the lowest layer, and interact instead with a saner level of API and modules in the language of their stack.
Sure, I know for a fact that what you're describing exists. That's not really what I mean by new business being built on it. That's a case of a very large and old business already being so locked into the mainframe ecosystem for their core systems that anything new they try to do ends up needing some kind of integration system with the legacy system.
What I mean is that nobody starts a business today and says "Ok, we need an IBM mainframe running DB2 and we'll have a bunch of COBOL, ReXX, and PL/I programs for handling our business logic".