The replacement time may be several weeks. An upgrade option might be a better path. The customer might be given a chance to obtain a better part than the one originally in the system. The upgrade would be the value of the new product less the current value of the old part. The customer would need to make up the difference in cost.
Downtime is usually a few days at most.
Option two might seem odd or unfair. The way PC's have changed in the last few years, however, paying a few dollars for the new version of a product makes much more sense than even trying to use the old part in many cases. Two years later it dies with a month left on the warranty. You are entitled to a used but working 1GB HD, but by today's standards, that is much too small to be of any use. It was fine two years ago, but no one makes anything that small anymore.