You mean like original Top Gear, 1977-style:no one, if they attempt to continue the show with a different cast I just wont support it. It be like any other offshoot top gear and not the original
Seriously, they could do a special edition featuring May and Hammond in order to show the remaining already-made features, with the Stig standing motionless in the studio. At the end the Stig takes off their helmet to reveal the new presenter...
...and if we're messaing around with the show's chemistry it could be a more radical change (Sabine Schmitz?), but it has to be someone with a big personality and car knowledge bordering on the obsessive. Chris Harris is good but I've always considered him to be much more of a Hammond replacement than anything else, and unless they're starting from scratch with three new presenters they'll be after an individual with a personality large enough to match Clarkson's even if not the same as before.
Top Gear will survive I'm sure, and I'm certain that producer Andy Wilman would have had ideas of his own as to how to proceed under these circumstances, knowing that Clarkson could depart at any point or be forced out after another incident. A complete newcomer as a Clarkson replacement would be a very interesting alternative as well, but that would naturally work best with May and/or Hammond still being there. Three completely new presenters would be a huge risk but still might work depending of course on who they have chosen.