They are not disincentivized from killing him. They merely are not being incentivized by a guarantee that the USA will have lots of sensitive documents released.
It should also be noted that an active dead man's switch opens the possibility that surveillance of Snowden will establish the mechanism of the switch, allowing the CIA to take over the switch and then do away with Snowden with impunity. By contrast the passive distributed key storage he likely has provides no active traffic that current surveillance can trace.
It should also be noted that an active dead man's switch opens the possibility that surveillance of Snowden will establish the mechanism of the switch, allowing the CIA to take over the switch and then do away with Snowden with impunity. By contrast the passive distributed key storage he likely has provides no active traffic that current surveillance can trace.