Hard drives fail. You are 99% ahead of the curve because you have backups. If you do image backups, you can restore the entire OS to the new drive and just boot (in most cases).
How to prevent a failed drive? Well, you can't. You can reduce the chance of a surprise by re-enabling SMART and checking it frequently - it's supposed to tell you when a disk is developing problems. You can reduce the pain by doing backups. You can buy more expensive enterprise-grade drives that have longer MTBF.