It is possible that VB6 apps won'twill not work when Win8 (or whatever it gets called) comes out. The company I just left got burned when Vista came out and the 16-bit apps stopped working because the VBXs could not be made to run on Vista. Microsoft decided to take out the native libraries that handle accessing Access databases. They can easily do that with the VB6 runtime library.
As a form of risk management, your boss should be considering updating the technology. Slowly moving piece-by-piece to .NET would make things much less stressful if MS decides to kill off the VB6 runtime. When new operating systems are in beta (usually called CTP), I strongly recommend getting a copy to install on a virtual to test your existing software. Vista was a shock to us, and that company didn't have a replacement for the 16-bit code for about a year after Vista came out - and we only knew it was a problem when customers starting calling to say it didn't work.
edit: while watching a number of webcasts on Microsoft Events, and in particular this one, I've come across the statement by more than one presenter that the VB6 runtimes will not be distributed in future operating systems.