Who will/can replace The King?
Jim Ross
Matt Striker
Josh Matthews
The Miz
Joey Styles
etc.
Let's dissect the names that you threw at the table (get it, table?):
Jim Ross: Ross already said it himself, he's "happy with where he is right now" in the WWE.
He COULD replace King, since Cole barely does play-by-play anyway and may be better off doing color commentating, but WON'T.
Matt Striker: Based on his commentary during ECW, I'd say that Striker's a great play-by-play commentator.
He could replace King and do play-by-play while Cole does color commentating, but I don't think they're gonna go with him.
The Miz: The Miz has proven me right that he can be an AWESOME color commentator, but I prefer him calling the wrestlers' moves since he's a wrestler himself. He could even do commentating when his career ends if he wants to.
He DEFINITELY CAN'T replace King since he's still wrestling and he definitely won't. And like what Jerichoholic8894 has said in his post in The Miz as a Commentator Thread:
I don't want him going on commentary full time until he's finished wrestling because I enjoy his ring work too much.
Joey Styles: I'm not familiar with Joey's commentating skills, so he doesn't apply to me.
Now for names that you didn't throw at the table:
William Regal: Regal is a WAY better play-by-play commentator than Cole. His calls on wrestling moves have been perfect - based on what I've been hearing from him.
He could also replace King and replace Cole's play-by-play while the latter does color commentating, but he also won't.
JBL: JBL and Cole had a great chemistry when the former replaced Tazz, so I don't see why the former can't replace King. It would be nice to see their roles reversed, with JBL doing play-by-play and Cole doing color commentating.
And although his allegiance is with the WWE, JBL's currently his own man right now - meaning that he'll be WWE's special guest at best.
With all of these being said, the only known person who WOULD replace King is Josh Matthews. Hell, Josh has been taking over King whenever the latter's not around, even at PPVs, which implies that the WWE has faith enough for Josh to hang around with the main commentating team.
I'm not saying that I enjoy Josh's commentating skills though. In all fairness, he just sounds too much like his mentor, Michael Cole himself: Bland.
Jim Ross and Joey Styles are 'play-by-play', just like Michael Cole.
Again, Michael Cole barely does play-by-play these days. Does a play-by-play commentator say "vintage" or "off the skull"?
For shame Michael, for shame.