Yes - if we need them to people can learn COBOL it's not any harder to learn than many other programming languages.
There are plenty of COBOL devs; they're just not in the American labor market.
Would bumping starting salaries for Cobol devs to 150k, resolve it in the US? (I am assuming banks could afford it.)
No, since that's not too much higher than starting salaries for Python programming at a medium-sized research institute, and there's no clear career progression for COBOL programmers.