Well the drive may fail sooner or later but its a good idea to get another. Yes, you can use the key on the sticker on the computer to activate windows. Better still, while the current drive is still alive, just save an image of the windows install using Macrium free or Acronis to an external drive, then you can just restore to the new drive- you wont even need to use the sticker code.
Imaging with free Macrium
Heres how to replace your hard drive:
Documentation