Because the final season is around the corner —
If you’re in a writer’s room on House of Cards after your star is forced out of the series, this is the greatest creative blessing you’ve ever received. You are now mandated to reinterpret your entire work through the lens of another character, and do so in a way that suggests it is the appropriate thematic conclusion to a story your audience didn’t even fully realize they were watching.
Pray that they don’t choose the easy spineless way. There are myriad ways one could try and distract, paper over his absence by telling the audience that all the supporting characters are just as interesting, give some credible but inessential plot device to explain where he went and then try to get people to focus elsewhere until you can wrap things up. But how much more fun — and what are the stakes, really, when no one expects this season to be anything more than a whimpering apology — to use his absence as a mandate for a major revolution, ask the audience to actually be obsessed with his absence, because it reinterprets the whole series for them. Swing for the fences.
E.g., Claire had Frank killed. This was always the plan. Every step along the way was her using him to get there. When all Frank’s sins are bared to the press at last, she can even admit to it while remaining the hero. Savior of the Republic. People buy it, evil ascendant.
Or, e.g., Frank was a suicide. Power and conscience unexpectedly overwhelmed him. Claire is shocked. But in the aftermath, as all his sins come out, she is overwhelmed by what she has been complicit in and resigns. Dedicates the rest of her life to healing the wounds that Frank caused, in part on her behalf.
Or literally whatever, as long as it’s revolutionary. If you’re stuck in this unsavory position of having to end something half-heartedly or do something bold and hope people forgive you for your transgressions, go bold. No half-assed hand-waving as you wrestle under your casting constraints. Embrace them, make them a gift.