How many miles can I expect to get out of my components?

[indysteel]

Every drivetrain--no matter how good--will need to be replaced to some extent over time. Chains, followed by cassettes and brakepads, cables and housing, are probably the quickest to wear. How long each of these items, along with the rest of your drivetrain, will last depends in part on how well they are maintained and on the conditions in which you ride. How well the drivetrain performs is also a question of regular maintenance. If you never get a tune up, your shifting and braking will get sloppy, but that doesn't mean the drivetrain itself is toast.

So, the short answer is that I'm not sure there's a good answer to how long your drivetrain--as a whole--will last. In my opinion, if you want a new and better equipped bike, get a new and better equipped bike. I wouldn't rest your case on your drivetrain simply failing. It won't fail on you--at least in any catastrophic way--unless you just take really bad care of it.