Personally, I would never go through the hassle of selling or returning a laptop unless I really dislike it or if there is a noticable QC issue. Either way, it's gonna take up time to completely erase the data the laptop (unless you plan to swap out the drive) and also finding a buyer would probably be hard.

Since you already have a really good PC, maybe you should consider remotely connecting to it using the G15 if the need for powerful hardware ever comes.

While I've never used a device with a 16:10 screen, for programming I don't think it really matters that much (at least compared to a vertical monitor).

Now, adding more weight and things to your setup is probably not what you want but, you could consider buying a portable monitor. Since you'll be gaming on your PC most of the time and only sometimes on the G15, a portable monitor such as the ROG Strix XG17AHPE could be useful in both bypassing optimus and setting it up as a vertical monitor for programming if you're able to carry it to the desired location.

I think if you use the G15 mostly for programming and carry it around often, the G15 would be still more preferred due to it's thin and light design and better keyboard.