Let me just save you some time — yes, yes he will be the final King of the Iron Throne on Game of Thrones. And with King's Landing looking to burn rather soon, perhaps literally if the theories regarding Cersei are to be believed, that end is going to come very, very soon. Once Tommen goes, the Iron Throne is pretty much up for grabs. And don't get it twisted — after that trial by combat ban nonsense he just pulled on Cersei? He is not long for this world.
And from his death, comes chaos. He has no siblings to pass on to. Which would result in a successor being decided by a Grand Council — only that's next to impossible right now when a number of lords are warring with one another, and Grand Councils are never convened during times of war. Which is to say, good luck getting lords across Westeros to meet up and decide a King.
It's just not feasible to suggest that you can get some of the most important people across Westeros to leave their many, many wars, and then try to decide what person they barely know should rule over them and the continent.
The other part is how the show quite directly pays lip service to a blood claim, but will always take the "might makes right" decision that basically means whomener's sitting on the throne by the time an army makes an approach on King's Landing is going to be multiple pieces across the city by nightfall. The only one who could truly hang on to the throne is Dany, and the only reason for that are her dragons.
No, the way Game of Thrones ends is to destroy the Iron Throne, melt it for scrap, and maybe turn it into a sword through which to stab the last King who sat in it. That's pretty much all you need to know about Thrones. This show really hates their kings. Meanwhile two lords are fighting tooth-and-nail over a crappy castle in the snow, and none of us can wait for that to happen.
More likely than not, you're going to end up with this jackass ruling you based off of some powerful general taking the throne and installing their weakling nephew. Everyone else is too busy fighting.