I have had some experience with mixing via wifi and will tell anybody it's not a comfortable feeling to see a "connecting" message on your tablet during a live performance. The last settings on the mixer will continue to work until the connection is regained, but there's no adjusting anything when the connection drops out until reconnection is made.
Not getting brand specific here, but a lot of the discussion about the various wireless mixers so far has tended to be around using an external router for better connection reliability compared to using the internal routers built into the mixers.
Some users are connecting through a router via ethernet and then also connecting via a tablet over the external router's wifi. If the wifi tanks, presumably the ethernet connection is still there....but I say "presumably" with a grain of salt. Haven't tried it myself. At some point, it's just not convenient to haul an external router, ethernet cable, PC, and a tablet although these mixers cut out the need for a multichannel snake and have useable compression, gates, reverb, and EQ built into a very compact box.
I was going to use my wireless mixer this week, and then chickened out to just use the venue's own analog board.