It makes sense, commuting to London from CA can't be fun. Chris Harris has the talent to keep the show entertaining, the risk is that the BBC will want a celebrity anchor and choose another Chris Evans to replace LeBlanc.
I could see Johnny Smith from Fifth Gear slotting in quite nicely as third chair. He was born the same year as Rory (1979) with Harris being 4 years older so it would be a team that, assuming it stayed together, would have a minimum of 5 years and probably nearer 10 to keep the show alive.
I honestly don't see the Beeb pulling the plug on the show. Sure viewing figures have dropped since the CHM days but that's mainly because they are carrying on with their silliness elsewhere and TG has reverted back towards being more of a car show than it had become in the final years of the Three Stooges' tenure.
Back when Chris Evans was on the show with Chris Harris, I thought it would be funny if they got Chris Barrie, just to make the hat trick. But I do think Chris Barrie could make a decent presenter, assuming he would even want the gig.
For me, some of the weakest parts of the post CHM era shows have been in the studio. They really haven't had someone who can present, interview and be entertaining to a good level, including having spontaneity. Clarkson was very good at all of that which is why the studio segments with those 3 worked so well.
Who the replacement could/should be, I'm not sure.