I'm writing the drum book for a local senior corps and at the end of the opener I want to have the cymbal line play a dotted eighth note flat crash followed by a sixteenth note crash choke. However, I can't figure out a way to get the ring of the crash to cease (I want there to be complete silence after the crash choke). I've tried experimenting with the MIDI controllers for volume and release to no avail. Is there any solution that anyone on here can think of? I'm using Cymbal Line 18in if that is necessary for y'all to know.

You should be able to enter C7,0 on that staff (or with ~ in front to hide it), effectively changing the volume to 0.

I tried putting that over the rest immediately following the sixteenth note, but it didn't take away the ring of the flat crash that lasts past the crash choke.

Since you're using Sibelius, you can use the Cresc/Decresc plugin (found in the Playback category of plugins I believe) to do this.  Simply add a decrescendo hairpin for your desired length of decay, then run the plugin on that hairpin.  The easiest way to figure out what percentage you should use for the higher value is to look at the mixer and see what volume you have the staff set at, divide that number by 127, then multiply by 100.  If you have it set at the default of 100, your value will be roughly 79.

That's a way of sort of hacking a decay, but there's not a way (short of modifying the original instrument in Kontakt) to do what you're wanting without some MIDI tricks.

This may not be your ideal solution, but if the sustaining crash is really bugging you, and there are other staves playing, you could substitute a crash choke for the regular crash. While that may not be what you want the line to play, using a crash choke would ensure the second to last note isn't ringing past your final crash choke. With other staves playing, it may not be too noticeable that the technique isn't exactly what you intend.