Step 1:
- Make a hard save in case it all goes wrong! ...
- Turn on God mode (Options - Game - God mode) so you don't need to worry about him shooting you later.
- Having the Gravity Gun makes body-dragging much easier than using the keyboard shortcut (which I could never get to work properly and have subsequently forgotten... possibly [L-Shift] + [E]?).
Step 2:
- Killing Crest won't be difficult, but it might help his attitude later if he doesn't actually see you do the deed. Try to snipe him from behind.
Step 3:
- Use the Gravity Gun (or the key combo) to drag him clear of the helicopter. Drop him in an open area clear of any obstacles.
- Make sure there are no mutants nearby who might want to interfere.
Step 4:
- Move close to the body until you get the "Search" prompt.
- Make a quicksave (the resurrection cheat usually crashes the game for me, but reloading and trying again often works).
- Press [ESC] then [R]. If it succeeds, Crest will be 'resurrected'. (Note: some 'dead' NPCs refuse to be resurrected and just flop down again; others may take several tries.)
Step 5:
- If Crest is now hostile to you (you did just kill him, after all...), then as long as you are in God mode you can ignore him shooting you while you use the Attitude menu ([ESC] + [F]). This should change his attitude back to neutral. Crest's name in the game's code is
puzir_crest, and this is what you need to enter in the Attitude Menu. If it works, you will get a success message, Crest will turn "yellow" and should return to the fire where you can talk to him again.
Afternote: I just tested the above method after shooting Crest in the face. He was successfully resurrected and remained neutral. Fun times...