First of all, if downtime is truly a concern, I recommend a clustered system using our redundancy and clustering architecture (see architecture diagram here and pricing here)
You of can course can have a cold standby system ready, and switch it over in case of failure of the first machine. Remember, a non-activated system will run for 2 hours at a time indefinately in trial mode, which would work in a pinch until you could call us and explain that the server crashed to get another activation for your CD-Key.