You need three cutscene-starting triggers: one for the truck ending (which checks that the players are still alive), one for the players dead (which also checks that the truck has not been destroyed), and one for whatever you want to happen if both events have occurred.
Use variables to ensure that once one cutscene has started, the other is switched off.
Init.sqs
1off=false
2off=false
cutscene1 script
? 1off : exit
2off=true
Cutscene 2 script
? 2off : exit
1off=true