Decompilers usually output massively unreadable code that needs a lot of decyphering and manual cleanup in order to be workable again.
Then again, some game engines do not even compile the game code to begin with.
We'd need more detail on how the game was made to give helpful answers - although I am reluctant to help here because tomas1235 does not have games on his account so I am immediately suspicious if he actually wants to recover his own game or steal / rip off someone else's.