It is possible to finish the game with solo character. And it's easier than finishing the game with a 4 character.

I finished the game by playing with solo character today. And it's easier than finishing the game as a group. I just created stealth based character. Before entering fight i am taking position at nice spot as stealth. Then "range attack - stealth - end turn" in same position until the mobs are dead. The monsters don't even move their position because they don't see you.

I hope they fix it. The fact that the mobs do not even move to find you when they do not see you makes the game very easy.