A database restore from a backup is a repair / recovery feature and not a high availability feature. If you are running a mission-critical system and if your database requires high availability, then please look into various H/A features available with SQL Server 2005.
If you are running a mission-critical system then you need your database to be available continuously or for extended periods of time with minimal down-time for maintenance tasks. So, the time required for databases to be restored must be kept as short as possible. Also, if your databases are large (VLDB's) , which may require a longer time to perform backup and restore then you SHOULD look into some cool features SQL Server offers to increase the speed of backup and restore operations to minimize the effect on users during both operations.