Would you kill the scientists before you died from the comet?
Absolutely not! There is an infinite list of reasons why you should not kill them; I'm just going to name a few here:
(1) I'm sure they didn't do it on purpose.
(2) Killing them doesn't chance anything because you are going to die anyway.
(...)
(n) May be just a nano-second before you die, the scientists somehow manage to stop the comet.
Second if you could kill the scientists before they launched the probe thereby preventing your later death would you?
Even the scientists don't know what happen next. If they know that would be their death, they wouldn't launch the probe in the first place. Since there is no way for you to know that would prevent your later death, it would be immoral and unethical to go around killing people because of what you believe may or may not happen.
Furthermore, even if your God give you the power to foreseen the future and tell you to kill those scientists, it would still be wrong for the following zillion reasons (to name a few):
(1) If your God is all powerful, why didn't he stop the comet in the first place? I'm sure he/she can just command it not to crash and it shall be done. If your God couldn't do it himself and need your help, then he isn't the powerful God after all. This is really a problem with the world today. Too many people saying that they do it in the name of their God or for their God or to save the world, but in reality, they are doing it for themselves.
(2) How do you know for sure that your God is the good guy? As far as you know, he may be the devil in disguise. Sure, even if he can show off some impressive powers, that doesn't mean that he is the good guy. If he is really all powerful and good, he would have stopped the comet himself.
(3) Doesn't it written somewhere that thou shall not kill? Especially, when thou doesn't know what is real and what is not. Saying that thou kill because of your faith or because someone told you so is simply a plain cop-out stupid excuse for thou ignorance.
(4) Since there is a thin line between having faith and having an hallucination, how do you know for sure which one is which? Oh yes, you are sure because you have faith. Isn't that arguing in circle?