How long does code last?

I'm in the process of going back over some of the more minor TODO's in my code. One of them is in a class that handles partial dates, e.g. Jan 2001. It works fine for dates that will be seen in our system (1990 - 2099) and gracefully fails for other dates.

The TODO that I've left for myself is that I don't handle dates in the century 2100 and beyond. I don't really think it worth the effort fixing this particular problem, but I am cognisant of the Y2k bugs. If we were in 2080 already I think I'd be thinking differently and would fix the bug.

So how long does code last for? How far ahead should we plan for our systems to keep running for?

Update

Ok, thanks for all your input. I think I'm going for the option of leave the TODO in the code and do nothing. The thoughts I found most interesting were:

• @Adrian - Eternity, I think that's the most correct assumption, your point about VM's is a good one.
• @jan-hancic - It depends, yes it does.
• @chris-ballance - I'm guessing I'll be dead by the time this restriction is hit, so they can come defile my grave if they want, but I'll be dead, so I'll just haunt his ass.

The reason I decided to do nothing was simple. It added negligable business value, the other things that needed looking at did add value so I'll do them first and if I get the time I'll fix it, but really it'll be nothing more than an academic exercise.

Longer than you expect.