I reckon JC will get the boot. He doesn't just do presenting though; he writes the scripts and his school buddy Andy Willman is the executive producer. Between them they drive the whole style of the show, the ideas, visual style etc. I reckon when Clarkson goes, May, Hammond and Willman will go as well and so will Top Gear in its current format. "Top Gear" as a programme might come back in a different format but it won't be (for better or worse) the Top Gear we know now.
Many shows have been restyled including Top Gear itself. I suspect it's going to have to be something really special if it can attract the audience and achieve international sales like this one has.