There is no way in hell Lexus will get rid of the GS. They might as well close shop and go home.
The GS sits perfectly between the IS and LS. Every car manufacturer has one.
BMW 3, 5, 7
MB C, E, S
Audi 4, 6, 8
Jaguar XE, XF, XJ
Cadillac ATS, CTS, XTS
Need I keep going?
What Lexus needs to get rid of is the ES Series. It has no place in their lineup. It is not that big a step up from a Toyota Avalon. Every dealership has been able to sell a Toyota Avalon over an ES because they can easily say, same chassis, same manufacturer the only difference is the trim and the badge. Which in all honestly is not that far from the truth.
Also, the car isn't even an option in some parts of the world, like the UK.
GS will stay but the ES may go.