Rewriting COBOL in javascript would make the codebase accessible to a larger pool of potential engineers who are also more likely to be up-to-date on best practices (as opposed to an engineer that has stagnated in COBOL for 30 years.)
I'm not sure a rewrite is warranted, but a system isn't maintainable if there aren't enough people trained in the particular language / tech stack.
I think conditional probability of a Javascript programmer knowing best engineering practices is so much lower than that of a COBOL programmer, due to large numbers of unqualified Javascript programmers, and much higher average experience of COBOL programmers.
oh please no JavaScript- it is awful enough in the frontend, but that train seems to have left the station, but in the backend we have much more powerful languages and ecosystems.
I'm not sure a rewrite is warranted, but a system isn't maintainable if there aren't enough people trained in the particular language / tech stack.