The system still runs the business. It is also on a version nobody supports, two people understand it, and the quote you got for replacing it came with the phrase feature parity and a timeline in years. This page is written from your side of that quote. What modernization actually covers, why the quote defaulted to a rewrite, what a rewrite risks, how to tell whether your system can be moved in slices while it keeps running, and when a rewrite is honestly the right call.
The system still runs the business. It is also on a version nobody supports, two people understand it, and the quote for replacing it came with the words feature parity and a timeline measured in years. You cannot tell whether that quote is the honest answer or the expensive one, and everyone you could ask sells the answer they give.
Here is the short version. Legacy system modernization is a spectrum, and a full rewrite is one end of it, not the whole of it. Most systems that still work can be modernized one capability at a time behind a facade, with the old system serving everything that has not moved yet and a way back at every step. The vendors that rank for this phrase almost all sell the platform that is their answer, which is why every one of them lands on replacement.
