You need to adjust said animation's events on the model. For this you'll need HL Asset Manager (HLAM)
- Load the model in HLAM and in the sequence tab/panel, load the animation you're trying to play.
- In the same tab/panel, check that Event #1000 is present in the sequence.
- If there isn't (or there is none), add one.
- Press "Add" button.
- Type in Event:
- Save the model.
Event 1000 tells the engine that the NPC dies in the sequence. At the specified frame, it presumably removes the NPC's collision and logic, though the sequence plays through the end. Then the sequence pauses at the last frame, its death pose.
I see a lot of stock scientist sequences having this event at frame 1, either because the player couldn't reach the scientist, or to make sure the player couldn't press E and cancel the animation (as they're already dead at the start of the sequence).
You might also want to check the "leave corpse" flag on the scripted_sequence.