“Upon falling into the world of his favorite game, a player running from his responsibilities joins a guild of adventurers on their quest, but when he accidentally releases the demon king from his ethereal prison, it is up to him and his new allies to defeat him.”

I think the problem this logline suffers from is that it tries to focus on two inciting incidents. To me the more interesting, the one that is the hook is the fact that he’s fallen into a video game. But since that concept has been used before, what does your story offer different? What’s the hook? The logline also uses vague descriptions. (for example, is it a video game or board game? Card game?) How would you describe the protagonist?
Why does he need to defeat the demon king? What’s his stake in this?

Example:?After he is sucked into his favorite video game, a gamer must help a guild of adventurers defeat a demon king who was released so he can return to the real world. (32)

My example also suffers from not giving the protagonist a compelling reason to fulfill this goal, it also lacks a compelling hook, but I tried to streamline your ideas. Here’s another attempt to tie things together better:

When a gamer’s arrival into the world of his favorite video game causes the release of a demon king, he must help a guild of adventurers defeat the king before he destroys everything, including the game itself. (37)

This version runs too long, but I added what I think could be an interesting angle, an interesting stake for the protagonist: if the demon king completes his goal, it will literally(somehow) destroy the game, his favorite game, meaning he can’t play it any longer. And I tied the arrival into the game with the release of the king.

I hope this helps.