Khabib would take him down and pass his guard. Believing anything else is being a GSP nuthugger, because GSP's wrestling is not on the same level as Khabib's. Moreover, Khabib employs sambo techniques like trips and throws in his wrestling from the clinch and these are additional tools GSP does not have. Khabib is also training with some of the best (arguably THE best) wrestlers in the sport as of now. While GSP's wrestling was top notch in the past, he is not on the level of Russian/Dagestani wrestlers and would get outmatched. The only way GSP can win this fight is by trying to keep it standing more often than not and eventually grinding out a split decision. It would be a tough fight for both athletes, but I see Khabib winning via a split decision.
First of all, Khabib's sparring partners are superior wrestlers compared to GSP and secondly, Tibau was roided to the gills. Tibau literally and I mean LITERALLY just fucking walked straight out of Khabib's takedown because of how strong he was.