My MBP is new so its not an issue yet. I was wondering though, if its 2 years down the road who is to say they back stock parts on older machines that far? If they cant fix it do they normally replace it with an equiv model out at that time?
Yes. if they can't fix it in a timely manner, they will send you a replacement based on what you had and what's available. Assuming, of course, you have applecare