It's not possible to cast/not cast based on buffs, anymore. You could write a script (there are probably already addons for it) that will make it really obvious that you don't have hawk on when you press the macro, though.
Another possibility:
/castsequence reset=combat !aspect of the hawk, hunter's mark, hunter's mark, hunter's mark, hunter's mark, hunter's mark, hunter's mark, hunter's mark, hunter's mark, hunter's mark
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