That doesn't matter for the countries were Nintendo products _are_ available. Also, the ease of rolling out those mobile games to those markets and build up brand recognition in those markets makes it easier to eventually do start selling their products in those countries. So it still contributes to their brand recognition in those countries.
And still, it's more directly aimed at their primary markets where Nintendo does officially sell their products.
You can't draw that conclusion from one game from one franchise. Echoes is a remake as well. And it's on an older system (3DS). Also, the sales numbers on their own really don't tell you how much of an impact Heroes might have had. But mainly the point is to increase recognition of their IP as a whole, not to boost the short time sales of one of their games.
You might see it that way, but that goes against everything Nintendo has said and done when it comes to mobile. They are very much intent on keeping the dedicated game system environment alive. And with their innovative controller systems, affordable price, and high quality combination of hardware and software they can certainly differentiate themselves from mobile.
The future isn't centred around mobile smartphones. That's a development process that is saturating very quickly. The next step is integration between many devices that form your personal network of devices. It's a big part of the internet of things and the internet of everything. That is where technology is headed now, and there is plenty of room for dedicated devices in that space. The concept of the Switch with it's flexibility in particular is well fitted for that world.
So, don't worry about worst case scenarios that are unlikely to happen. You might as well say the worst case scenario is that Nintendo is doomed to go under. It's pointless really. Possibly a remnant of last gens mindset.
