A few ways things can go:
1. When confronting Moro, Gohan recommends they don't mess about as magic is dangerous to deal with. Vegeta, or all 3 Saiyans, kill Moro before he can fully drain them and quickly end the arc.
2. Things go the same, with Gohan's energy making Moro significantly more powerful than before. I still think Gohan would return to Earth due to just getting in the way of Goku's training to achieve UI and Vegeta being more apt to use a skilful Yardrattian technique. At most, this additional time and knowledge of how dangerous Moro would be may cause him to train more intensely with Piccolo and probably learn the Mafuba due to knowing conventional fighting isn't the best way to approach Moro. During the battle with Saganbo, things go one of three ways:
A. Gohan uses the Mafuba to seal Saganbo, forcing Moro to take the stage. This does mean Gohan, Piccolo, #17 and #18 may be killed before Goku arrives, though whether or not this will affect the arc going forward is up in the air right now.
B. Gohan finds an opening to seal Moro, assuming the difference isn't so much the Mafuba wouldn't work. With the additional training as well as Saganbo's power source possibly being severed, Gohan and co. defeat Saganbo before Goku arrives or Goku defeats him easily upon arriving.
C. Due to the Mafuba not being effective against Moro or Saganbo, the arc's main plot remains unchanged.