I had to cut off an audio file abruptly once, and I found that I could smooth out the abruptness by quickly fading in a reverberated version of the audio, just as the original audio was about to end, and then letting it ring for a fraction of a second after the original had ended.

(I say "fading in", but it might have been that I had the reverb applied but dry, and transitioned to wet just before the signal ended.)