I'm guessing the app was created to give them extra time to get a working alternative. Flash is not scheduled for burial until December 2020 if I remember correctly. Most browsers from what I've read will have stopped support long before then. If Plarium doesn't get the new engine ready by the time the last decent browser drops Flash support for good, and I've not come across any information yet that leads me to believe that they will, the app will probably be the only way to access Stormfall in 2020.
I wonder if their problems stem not from getting a working engine, but getting the engine to accept the current player data for carryover. It won't surprise me if they one day come out and say SF will continue, but will require a complete wipe.