In the following sentence, is it appropriate to shift the tense? (The tense which is shifted is in italics);
They were lucky enough to have escaped the clutches of the Giant. However, they had suffered a tremendous loss. Their resources were reduced to ashes and now, they have just lost their leader. Without their leader, they were nothing.
Is the usage of have correct? Does it have to something to do with the word now? If it's wrong, please state an alternative! And if possible, please explain the usage of verb shifts.