I've been involved with several legacy systems. We scrapped a couple and started over. We ported a couple more
to new technology.
The decisions involved several factors. How critical is this system to our business? How much work is involved in
creating a new system? Are there dependencies we can't do anything about? What happens if we don't do anything?
Of the projects I've been involved in, we scrapped a couple of legacy systems and started over. One was core
to our business but ran on bespoke abandonware. We threw out a hideous hideous excuse for a network
management system and made a new one from scratch.
A closely related application wasn't as big a part of our business
as the original developers thought it would be, so I ported it from VxWorks to Linux. No business case for doing anything more.
Another biggie was porting device firmware from Sun Programmer's Workbench to Linux and gcc. No business
case to change the hardware (core to our business), so the software had to adapt.
Some the new systems are over 15 years old now and almost qualify as legacy systems themselves.
They've served us well.
...laura