Your team is stranded. Your mission is critical. Your leadership is your only chance. Will your supplies last? Will your team? Do you have what it takes to see this through?
This is where I think the focus should go on the tagline, even if what I've come up with my be cliche or terrible on it's own.
This puts the focus on the player, and hopefully gets across the point that not only is the player responsible for this super critical mission but also responsible for its execution and the lives under their command. When you talk about the Prince Roger series one of the things I really hope you are trying to capture from it is the sense of responsibility that Roger grew to feel towards his guard troops balanced with the absolute necessity to spend their lives to achieve the larger objective at hand. Big missions to save the everything are standard, especially in gaming, so we need to focus on what makes this one different, and unless I've been reading this wrong thematically, I think that's where you'll find it. Not many games put a face on the guys you send to their deaths, and rarely are these troops your most limited and valuable resource, and in Roger's case, his closest friends and companions.