Whenever people see old systems still in production (say things that are over 30 years old) the assumption is that management refused to fund the replacement. But if you look at replacement projects so many of them are such dismal failures that's management's reluctance to engage in fixing stuff is understandable.
From the outside, decline always looks like a choice, because the exact form the decline takes was chosen. The issue is that all the choices are bad.
Don't replace an existing solution with exactly the same thing on a different platform.
Think larger. Solve today's / (near) tomorrow's problem's BETTER. That's probably going to require changes to process too. A full evaluation of what's the most effective way with the capabilities and needs that exist now.
Then bring up interfaces that provide what the old system did, verify the data round trips, and when it's approved cut over.