Happened with Apple, too, after the OS8 debacle. Interestingly, Apple ended up with a greater market share after that change, even though they jettisoned the past user base more thoroughly than MS did by moving from VB6 to VB.NET (conversion, even by hand, isn't terribly difficult unless the program being converted is enormous). So, there are cases of applications and companies disappearing when they abandoned past users, but one shining example of a company who abandoned continuity and came out stronger for it. Furthermore, there are examples of powerhouse programs that did NOT abandon continuity and still ended up in the wastebin (Lotus 1-2-3 and Borland's Quattro Pro are two that come to mind).

So, some companies died if they maintained continuity, some companies died if they abandoned continuity, and some companies thrived while abandoning continuity. Therefore, when is it essential to maintain continuity?