Where I work if there is a physical fight of any description both parties are liable to be sacked. The view is that it takes two to cause an arguement and both sides are as guilty as each other.
The findings of Ken MacQuarrie's investigation
http://downloads.bbc.co.uk/mediacentre/investigation-summary.pdf seem pretty unequivocal that this was not a "fight." It was an attack, verbal and physical, and "it is the case that Oisin Tymon offered no retaliation."
The BBC have no option but to sack him. It is a complete failure of "talent management" at the BBC, rather than a failing of the Top Gear production team or anything else. Clarkson should never have been allowed to boil over in his ranting to the point of a physical assault; the broadcaster had already backed itself into a corner by giving him a well publicised "final warning" so when he kicked off again, in whatever form, there was really no other course of action available.
I'm sure TG will limp on with other presenters. They need to be properly passionate about cars, have a decent pedigree in motoring journalism, and the personality (individually and as a group) to engage an audience. VBH? Jason Plato for the May-esque sensible engineering bits? Chris Evans' name is being bandied around a fair bit - not sure that would really work. Johnny Vaughan? Actually, given that Vaughan has done a chat show and could do the star-in-a-reasonably-priced-car section well enough, that could mean VBH and Plato doing the more serious driving stuff. Could work... Oh, and Butler-Henderson is married to the current series director of Top Gear. I'm sure he could put in a quiet word
It'll be interesting to see what happens next.
