In a mostly proprietary environment that's really hard to say. In the world I live in (Germany software business world) few things get really deleted once they

In a mostly proprietary environment that's really hard to say. In the world I live in (Germany software business world) few things get really deleted once they made it into the daily life of a company. Nearly all companies have code that was written like 5 years before their foundation by one of the glorious first 3 guys and that is still used in most of their major software products. The tricky part is getting even awesome software into these daily routines. Hell, I'm quite sure that some of the first software I wrote is still used in SAP despite me never having worked for them.