As it was explained to me, "Talk Around" is to be used when the repeater temporarily unavailable or has dropped out for "whatever reason." Using Talk Around on the MXT400 continues to use the simplex channel and any tone set, the repeater would have output on so, your group can continue to communicate but, without the use of repeater. In essence, the radio just drops the input signal to the repeater when you select Talk Around. This way the group does not have to swap channels or tones in absence of the repeater.
So, to use the "Talk Around function" everyone in the group as to be, or get, into that mode in order to communicate. It's not like the leader of a pack in the woods is the only one to switch. All has to switch.
My question for Midland also was, How do you get everyone to switch into a talk Around Mode" Past the word to the closest behind you. "Once, everyone goes into "Talk Around" mode you can stay in it or if the repeater come back, swap modes again to use the repeater.