To be honest, I could EASILY see this being the setup for a Count Emmanellain scenario. Emmanellain has gotten a lot more in the way of character development than Artoirel has - the latter has always been the "competent" brother to measure Emmanellain's incompetence against, with little in the way of development of his own. Emmanellain is comfortable in his lack of responsibility, as he knew he could depend on his brothers (now, brother) to handle important tasks. Emmanellain has also gotten some hard lessons on the consequences that can ensue when he IS given responsibility, and wields the power poorly.

If Artoirel is killed, his comfortable buffer is gone. There's no one else - he's the last and only choice to become the count. Emmanellain will likely be very distressed by this, as it is unlikely he considers himself to be qualified for the position. He'll have to grow up, and fast. The buffoon will have no choice but to overcome his buffoonery, for the sake of his family and out of respect for his fallen brothers.

To be frankly honest, from a storytelling perspective, Emmanellain becoming the final heir has a WHOLE lot more potential than the status quo, with boring ol' competent Artoriel taking over and Emmanellain living out his days in his safe, comfortable bubble. That said, given that Ishgard is no longer the storytelling focus, I could easily see the writers having too many other pies to attend to to bother spicing up the Fortemps drama. The status quo may well remain as-is.