See, I think that If this were to happen (not saying I want it to by any means) That it would be more like this:
Hummer/Jeep together
Chevrolet still as the mainstream total volume brand.
Dodge REPLACES Pontiac eventually. (I mean be honest, they are in the same market position as a Sporty brand and Dodge does sell more and has a better image than Pontiac)
Saturn for Import fighting.
Chrysler REPLACES Buick (Again, same sort of market position, but Chrysler has a slightly better reputation)
Cadillac still as the flagship
The only answer I don't have is for GMC. I mean, You should put Dodge and GMC together and do away with one truck line. But that doesn't seem likely to me even in my own hypothetical evaluation here.
But Lutz has said that Pontiac and Buick are damaged, and really not a lot is happening to either except for Enclave and G8. I think that it would be smart for GM to consider doing away with them IF they do buy Chrysler.
Just my two cents though.