Ok the good hero has reached lv 99, killed the big bad and finished the game, now he is in a world where his role as a killing machine ceases to exist.
There cannot be a happy ending, he cannot settle down and have a family in the first place, he pressed the "skip" button in every romantic scene, thinking them as boring and mundane. Ok, for those that disagree with me, he may have found them "charming", but not something he wants to spend their whole lifes with. He knows he is destined for something greater and not the mundane life of a commoner. For the superhero it was ok to leave his family for weeks in order to deal with the big bag.

His wife would not be in a mood to a) worry if hero dies every time b) be alone for weeks because the hero is in adventure c) waste/steal the hero's time, when he could have used it to save innocent people d) risk her whole family safety because the next villain is sure to attack the hero's only weak spot (his family) e) 99999 strength means he is prone to doing accidents and how would one do sex with that kind of power?. His wife would certainly sooner or later leave him.

As time passes the hero's role diminishes even more, instead of killing villains, he is now left in a peaceful world where he can only perform minor volunteering works :
a) get cats out of trees b) help by lifting things etc.
His presence is strong, people now "worship" him as an idol, everyone is his fan, and everyone tries to be like him. There is no criminality !!! who would dare to
steal something knowing that superman with 99999 speed can catch him in a blink of an eye, no matter where he is (even at the other side of the world). Which means that his main entertainment "combat" is removed forever from his life.

People are now reliant to the superhero, for every minor thing that happens they ask him, e.g a pin falls down "superman please help me find my pin", and now they expect him to come instantly and help them because of his superspeed, x-ray vision, and ability to hear everything anywhere in the world.
From a savior he ended up as a desire fulfiller, why would people try to do something themselves when they can ask superman to do it with no strings attached. Not to mention the fact that people produce more and more desires, the faster they are completed. Well you do the math, what is going to happen.

He has to be on stand by, hearing everything people say all the time and filter them based on their importance.
Does he get time for himself ? No, he doesn't. He wanted to please everybody with his naive mindset and was happy to press "yes button" in every quest before. However he can no longer continue doing this, his physical stamina begins to deteriorate, he has worked overnights without sleeping, just to help every possible being. And when it refuses, it happens. "Why not me ? You helped that beggar that asked something much harder and not me ? i though you were good ? and now you abandon us ?". Riots emerge "give us our old superman".

He stages his death in order to avoid all this madness that he never asked in the first place.

Question :
Games finish the game with a happy ending (everyone is safe, the hero marries the woman of his life) and then they throw the credit screen to avoid answering what happens next.

1) What do you think would happen if there never was a "credit screen" and the game continued ?

2) how would the hero's past actions influence the world?

3) Video games with "good heroes" always follow the same persona, a) i never do bad, b) i love everyone c) i always say "yes" to quests, to my superiors and do what people ask completely disregarding myself.
a) is this feasible ?
b) is this a video game propaganda ? to turn us into mindless slaves ?
For instance in WOW: if you dont say "yes" to a quest", you dont get the +1 strength candy.
You are expected to mindlessly follow orders to reach the "destination" lv 85, be it to kill 85000 rats or finish 8500 quests.

1) There's a pixel art video out that does a pretty good spin on this exact subject. Personally I always thought it would turn into a version of the Sims but with less antisocial behaviour.
Found the video:Link

2) Would probably just be remembered fondly have some statues built and then everyone would get on with milking the cows.

3)

a. Feasible? Well yes it's one of the most tried and tested hero "types". Although they are often more 3 dimensional than that.

b. No defiantly not. It's just what people tend to like aka a happy ending. I know if I get into a story I enjoy everything wrapping up nicely in the end. I really don't enjoy the whole characters dying and people being c**** so it can be "different".

WoW is a poor example to use though. It's the mechanics and design of the quest system that cause what you said to happen.

I gotta tell ya. I really tire of anti-heroes. Every archetype can wear out its welcome. Every joke is eventually not funny if you hear it enough. At some point, anything can be overdone.

But per your story and setting... Our good hero views combat as entertainment? Our good hero has little respect for his own wife? Then the laws of nature would have it that criminality would not disappear. This god amongst men would be imitated for certain, and imitation often inherits imperfections with interest. So that little room for imperfection in our good hero would still breed something rotten into the world. A little leaven ferments the whole lump.

Should the hero realize that this is the case, then he would have to also realize that all his conquest was in vain. His crusade against evil was all striving after the wind. He would have to either make peace with this somehow, or decline into cynicism. Should he choose the latter, he may choose destruction just as easily as exile.

If the hero is smart, he will create a corporation to prevent liability, hire people that will deal with the minor issues while he sits at the top looking all important, rakes in the cash and retires on some tropical island. Since the big bad evil guy is gone, his underlings can take care of the day to day business.

I'd love to see that shareholder's meeting.

I dislike games that makes you to powerful. As soon as nothing could touch you in Skyrim, the game got boring.

1) What do you think would happen if there never was a "credit screen" and the game continued ?

That depends on what elements you introduce. You might put the hero down on the path to becoming a villain, but that's quite a long way, as by what you've told, you've spent an entire game convincing he's not a villain, but a "zombie" good person.

2) how would the hero's past actions influence the world?

Villains are put under more pressure, and so they become more extreme. The "normal" society might turn into something less pleasant. A government turning into a totalitarian suppressive one for instnance. Say the superman story would not be in USA, but in germany (prewar). He would be the good guy, fighting crime etc, while the society around him gradually turns into a nazi state.

As far as I remember in Blizzard's Diablo 1, after Diablo is defeated, the hero becomes the next Diablo of the sequel.