Plenty of services can deal with X hours of downtime when a single machine fails for values of X that are longer than it takes to restore to a new machine from backups.
Heck, even a machine like that being down for a week is usually still worth it.
And anyway if you already have all in place to completely rebuild every SPOF machine from scratch in a few hours, go the extra mile and make it an active/passive cluster, even manually switched, and make the downtime a minutes thing.
Single machines just don't fail that often. I managed a database server for an internal tool and the machine failed once in about 10 years. It was commodity hardware, so I just restored the backups to a spare workstation and it was back up in less than 2 hours. 15 people used this service and they could get some work done, without it, so there was less than 30 person-hours of productivity lost. If I spent 30 hours getting failover &c. working for this system over a 10 year period, it would have been more hours lost for the company than the failure caused.