Complex sentence: Now a vampire, she prepares to bite him as he leans down to kiss her, but instead he drives a stake through her heart and kills her, then leaves with Mark, overcome by grief and knowing that the vampires will continue to pursue them.
Split into simpler sentences: Now a vampire, she prepares to bite him as he leans down to kiss her, but instead he drives a stake through her heart and kills her. A grief-stricken Mears then leaves with Mark, knowing that the vampires will continue to pursue them.