There's claims that Attila comes from Gothic and means Little Father. If Hunnic kings used Gothic names, it could indicate that Gothic was widely used by the Huns at Attila time. I would not find it unlikely that the Huns having conquered, ruling and allied with a host of different Germanic tribes, most of them East Germanic could have adopted Gothic.
As for Hunnic survival, it would demand they moved out of the Pannovian plains. That's a area which get regularly overrun.
So my suggestion are that Attila end up attacking the East Romans, conquer Constantinoble, and settle the Huns and some subjected/allied Germanic tribes in northern Bulgaria and in Wallachia. As Attila dies, his heirs doesn't alienate the Gepids (who was the main henchmen of the Huns who kept everyone else in line). As the Huns need their Germanic subjects to keep control over their new possessions, the Huns and their Germanic subjects slowly assimilate into a new tribal confederation, who call themselves Huns but speak Gothic.