Something like what was done in Awakening with the Outrealm character units? Maybe so! And optionalising permadeath made the series less obscure and more accessible to lazybones newcomers as we've seen with the latest two 3DS entries, so my guess is that especially because it'll be released on mobile devices, disabling permadeath will probably still be a feature to appease the more casual mobile players.

As far as images go, we've only got this placeholder logo. Latest news was the initial announcement of the FE mobile game and the one set in the Animal Crossing universe already dates back to 27 April. So far still nothing to note, and I wonder how they're going to manage microtransaction options. Also, will it take place in a whole new universe or one of the existing ones (like the relatively unexplored Sacred Stones' world of Magvel...)?

Think I'll be playing this during the long waiting game:
http://serenesforest.net/2016/11/24/tearring-saga-full-translation-patch-project-compete/

As of what I've seen in the Direct a half hour back. your prayer has been answered @Zaphkiel: no sign of permadeath in Fire Emblem: Heroes!