Having had to re-implement a few legacy systems in newer code for nothing nearly as complex or with as much risk as what you're referring to, I can't imagine any dev not screaming and running for the hills if asked to do this. The chance it will work correctly without bugs early on is close to nil, and the downside for bugs when dealing with financial systems makes the risk analysis being as large as it is, it's pretty clear cut.
I keep telling myself one of these days I'll get to reimplement some system that has good test cases, but I know that will never happen. Any system that is designed well enough to have good tests doesn't really require rewrites in the vast majority of cases.
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Having had to re-implement a few legacy systems in newer code for nothing nearly as complex or with as much risk as what you're referring to, I can't imagine any dev not screaming and running for the hills if asked to do this. The chance it will work correctly without bugs early on is close to nil, and the downside for bugs when dealing with financial systems makes the risk analysis being as large as it is, it's pretty clear cut.
I keep telling myself one of these days I'll get to reimplement some system that has good test cases, but I know that will never happen. Any system that is designed well enough to have good tests doesn't really require rewrites in the vast majority of cases.