He only returned to his magic tower after he had refilled the arrows. He was not expecting to kill 3 elite wizards here. The 'Mana Burn' from hell was a lot more powerful than he thought.
By that point, Johson had already become a bone chilling contracted beast. Once this news spread, he would be fully exposed to the world.
Abel planned to unleash Flying Flame as well, but luckily, Flora resolved everything by itself. Therefore, Abel could still keep it as a secret weapon.
All the effort he had put in his magic tower did not go to waste, after all. Flora could not have done this if it didn't have so many little war puppets and Bursting Crossbows.
Those wizards who came from outside the Holy Continent were actually the men Wizard Cliff had threatened Abel with. This caught him by surprise. Originally, he thought he had already resolved the situation with Wizard Cliff; he never thought it would bring about more elite wizards.