I don't know much about midi files because I almost never used the midi editor but as a start it would be good to know how to fade out a recording , instrument
Drag the upper right handle of the midi object to the left. This is the fade out handle. There is a similar fade in handle at the left. Same as for an audio object.
To a limited degree, modify the velocity (volume) in the midi editor by drawing to reduce the velocity of the notes near the end. Each note has a velocity, so if there is a long sustained note at the end, it won't work.