Even if we intentionally released as much co2 as we could all life on earth is not at risk. Remember that there's a fair amount of life that is virtually unchanged since the paleozoic period when all that co2 was in the air. Beyond that there's stuff that hangs out in volcanic vents, rapidly evolving life that can adapt even to rapid change, bacteria, molds, mosses and algae. And who knows maybe there's even a small adaptable mammal or 2 that gets out and evolves enough for a second attempt at sapience.
Don't get me wrong the climate disaster is truly a unique and devastating extinction event, but humans are not so powerful as to leave the earth a completely lifeless rock.
Depends on how old the game is and how big the DLC is IMO. Rimworld, for instance, has quite a few DLCs now, but they are all well worth it if you like the base game. OTOH if a game just has cosmetic DLC or the DLC is coming out super near release that's a red flag.