At work we're in the position where three of our main competitors are struggling bad after all trying to rewrite their software. Good for us, we've captured a number of their clients due to this.

We've instead focused replacing parts of the program over time. If we touch some old code that works but needs to be extended for a new feature, we usually rewrite it and bring it up to date as part of implementing that feature. Other times it might be too sensitive and we just modify a small piece of the old code and let it chug along like it has done for over 15 years.

Instead of spending time rewriting the whole shebang we can deliver features, alternatively not having a second team reimplementing everything avoids a huge financial burden.