Those hoping to see Thanos in the upcoming Guardians of the Galaxy game will want to temper their expectations, as it seems he's actually already dead. The infamous Marvel villain met his match prior to the events of Marvel's Guardians of the Galaxy, which may come as a surprise to fans who saw just how formidable he was in the last two Avengers films. That said, it sounds like he didn't go down without a fight.
Eidos Montreal is taking a lot of creative liberties with the Guardians of the Galaxy as it wants to ensure there's no confusion between this version of the cosmic characters and the ones in the MCU. Similarly, there's no cross-over between the Marvel universes that Insomniac Games and Crystal Dynamics are building independently of each other. As of right now, Marvel's Guardians of the Galaxy is a contained story with no relation to other games. So, the likes of Thanos can still appear in those other universes should those developers go that route.
Thanos will probably not be appearing in Marvel's Guardians of the Galaxy, however, as Drax killed him. According to senior creative director Jean-Francois Dugas in a PlayStation Blog, prior to the events of Marvel's Guardians of the Galaxy, Drax killed Thanos in an act of revenge after the Mad Titan murdered his family. Ultimately, his quest and obsession for vengeance resulted in tons of destruction which led to Drax's imprisonment. Upon his release, he was recruited to join the Guardians, where he seeks to redeem himself for his recklessness. Dugas' blog post indicates that Drax doesn't believe Thanos is truly dead, however, which might hint at a return for the Mad Titan after all.
It's clear that Eidos has created a rich world for players to dive into this October. Every character has a unique backstory, and the developer isn't trying to mimic the MCU too deeply, even if there are some similarities such as Star-Lord's usage of music. In another similarity to the films, Drax maintains his somewhat oblivious personality in the game, so fans can still expect him to provide some levity even with his tragic backstory.
Whether or not this sort of history will impact the relationship or dynamic between Drax and Gamora, the adoptive daughter of Thanos, remains to be seen. Either way, it highlights just how much effort Eidos is putting in to make sure Marvel's Guardians of the Galaxy is different to the MCU. While it's a bit sad fans likely won't get to see this universe's version of Thanos, it will hopefully allow the developer to focus on characters fans of the movies may not be quite as familiar with and create a really original story.
Source: PlayStation Blog