and another attacker who is right next to the goalkeeper, blocking the goalie's path to the goal.

The attacker with the ball shoots the ball through the air into the empty goal, with not even a tiny chance the goalkeeper could ever make it. Is it offside?

It's always context dependent, your version is fairly extreme in that the GK wouldn't be in a position to jump and use his hands to maybe make a theoretical save, but a player in offside position would be interfering with the play. It would be up the ref team to make a subjective call.

Maignan was pointing towards Dumfries almost before the ball had hit the net, it was clear interference even if the GK didn't stand a chance.