Speaking from experience, the main office (111 8th/76 9th) is amazing. I think Google's decision to buy that years ago has totally been vindicated. I'm surprised more high cash surplus companies don't do this, just to control their destiny in a way you simply can't as a tenant (eg if you're a large tenant, each floor you rent in the same building is going to get more expensive, being a tenant limits what you can do).
Other posters have pointed out the Chelsea Market is a mishmash of other buildings (4 IIRC). All true. It's a super-annoying building to get around in though. To get from the 6th floor on one side to the 6th floor on the other side you might have to go to the ground floor and find the right elevator (out of like 20 in 12 different locations) that goes to that floor in that building. Some parts are only served by a single elevator. Others have a bank. Honestly I'd hate to work there, particularly if you had to go through the crowds to get to your one blessed elevator.
One outcome of this might be that Google may well fix this situation by combining floors and elevator banks.
I don't think anything will happen to the ground floor of Chelsea Market.