If they died, Nintendo would loose out on a possible revenue stream in the future. This is why some of you aren't business heads, although I can't speak too well about Nintendo's business right now either...
Still, they should be kept around in some form. I think we might see Miis in the future on Nintendo's dedicated consoles because they like to use them for your accounts and as extra characters in games, but the Wii series might be relegated to mobile play or possibly QoL. However, we know close to nothing about QoL so I'm completely guessing.