What sequel, if any, would you write to fake married? What effect does the showy gold-braid-packed wedding have?
As goldenhart's "A Political Affair" suggests: Hornblower in his pessimism failed to take into account his own celebrity; he furthermore failed to take into account Barbara Wellesley's social acumen and connections. When the Duke of Clarence made an appearance at Bush and Hornblower's wedding breakfast, thereby signaling royal approval, the moment was ripe for Society and Admiralty perception of military marriages to tip.
And it did. Slowly. Ponderously. There were still plenty of old guard who looked askance at the marriage, but they no longer held the complete sway over opinion that they once did.
Consequently, instead of being beached, Hornblower is given command of the squadron being sent to the Baltic, and is further permitted to take Bush as his flag captain. Nevertheless, Hornblower is very aware that his appointment is a test case: a chance to excel and prove the old guard wrong in their prejudices -- or, if he fails, to inadvertently set the cause back by a decade or more, making life very difficult for anyone considering following in his and Bush's footsteps.
Thus we come to the story of the Baltic mission, the overwhelming pressure on them as poster husbands, and the difficulties of navigating the twin spheres of being both spouses and commodore/flag captain, and new to both sets of roles, to boot. Remember how weird Hornblower is in Commodore about ostentatiously demonstrating to everyone that Bush will be shown no special favours? Hornblower is so determined not to let their being husbands fuck up the mission, that he risks the cascade of instead fucking up their marriage, thereby fucking up their working relationship, thereby fucking up the mission after all. (Remember the bit about Hornblower watching Bush sleep through the gallery windows? Someone got sent to sleep on the couch for being an asshole and is having regrets about it.)
Unfortunately, just as they're figuring it all out, Hornblower falls ill with Typhus...