Make a multimanager that will target the scripted_sentence that will make the scientist talk and after a few seconds make the multimanager target a aiscript, that will make the scientist play a death animation(action animation) with the leave corpse flag.
If you want the scientist talk while he is sitting on the floor,like in the blast pit, make a multimanager that will target a script at the beginning of the level(a trigger_auto,with the trigger state set to on, will target that multimanger) that will make the scientist play that sitting idle animation. Place in front of the scientist a trigger_once that will target another multimanager. That multimanager will target a trigger_relay, with the trigger state set to off, that will target the first script.(the one that plays the idle animation) after 0.1 seconds(not less) it will trigger a second script(or aiscript if you don't want it to be interapted if you shoot the scientist) that will play the action animation,the one that the scientist talks and dies afterwards(check the leave corpse flag). At the same time that the multimanaget will target the second script it will also target the scripted_sentence that will make the scientist talk.(remember when using scripted_sentences always write the name with capitals and with a ! before it)