But then why do they have a controller at all? From my research you lose at least some of the functionality of the network- for example, if CWP is stored on the Meraki server and you lose connection, obviously you cannot authenticate users that way. I would argue that the features that aren't lost probably aren't there anyway, i.e. , L3 roaming, load balancing etc. With regards to local data traffic, if access to the controller is lost, local forwarding only works for those already connected. If they then try to roam, they'll fail, the same goes for if they try to reconnect.
If you're going for a controller based solution, it's better to go for a physical device on site IMO, it's less likely to go down that your net pipe.