Doesn’t exist within Cantabile itself, but there are some tricky solutions that you can use to achieve this.
Simplest solution is to record a MIDI file with a timed controller fade from 127 to 0 and use this in a media player to control your instrument volume. Use a binding for “play” on this media player and let it run its course.
I’ve built some ReaJS scripts to create smooth controller fades - you can also use them to do this, e.g. this one
And of course, there’s @dave_dore’s famous auto fade rack: