Perhaps Mitch has been an android like corpse for a long time and now they just can't keep it going becuase his organs are gone. His mind was obviously gone a long long time ago.
And thus now that his body will die the electronics that they used to control his voice won't have a host.
and so they have to have him 'die' even though he's been brain dead for a very long time. Samething they did with Ginsberg.
of course I know that this is far out and many say 'implausible' but I say that technology is very advanced, especially the stuff that doesn't get put out to the public by spy agencies.