This cannot be answered in general. I heavily depends on your workflows.
Wikipedia has a great table that shows you how much time you can be "down" to reach the 99.99% availability (High availability - Wikipedia ). So it depends if you are running windows servers that need regular patching (the reboots will be downtime, unless the solution is clustered).
From the vsphere point of view, thanks to vmotion and the cluster HA you can achieve a very high HA level. but this isn't really vSAN related, this is true for every storage type.
