I have no idea how much time this would take in the real world. Pulling a number totally out of my ass, let's say five years. You may not use subcontractors to develop the software.

Well, then I'm pretty confident I could survive at least five years... :P

Which I guess is enough time to buy life insurance. At least your family won't have money problems. :-)

To be honest, for commensurate reward, I'd probably be sufficiently confident that I could get something done bug-free in 5 years if it was something that I felt could hack out bug-full in a week. Much of that time would go toward task-specific verification-related tooling...