I think regardless of how you view homosexuality, gay people do exist in the wider world, so it seems to me like they should exist in gaming fiction unless you make a specific decision to edit them out of existence. It's like if your game series has no blonde people in it anywhere. It might not jump out at you at first, but eventually you'd start to think "I feel like there's something...missing..." Sometimes context might let you get away with it...if you're especially anti-blonde you can set your story in China where 99.78 percent of Chinese people have black hair (thanks wikipedia), but even then I'd probably raise a sceptical "how conveeeenient" eyebrow.