Would a team be able to utilize <G17> to handle their robot and put the cube/ball back into play, or should this cube/ball be considered to have left the field?
In the future, please quote the applicable rules from the Game Manual so that future visitors can have a better understanding of a question's context.
G10 states the following, with a portion bolded for emphasis:
<G10> Keep Game Objects in the Field. Game Objects that leave the Field during a Match will not be returned. “Leaving the Field” means that a Game Object is outside of the vertical projection of the Field Perimeter and no longer in contact with the Field, Field Elements, other Game Objects, or Robots.
G17 states the following, with a portion bolded for emphasis:
<G17> Handling the Robot mid-match is allowed under certain circumstances. If a Robot goes completely outside the playing Field, gets stuck, tips over, or otherwise requires assistance, the Team’s Drivers may retrieve & reset the Robot. To do so, they must:
a. Signal the Head Referee by placing their VEX IQ Controller on the ground.
b. Move the Robot to any legal Starting Position.
c. Any Game Object being controlled by the Robot while being handled must be removed from the Robot and gently placed in a non-Scored position by the Team.
d. Any Game Objects in the Starting Position may be moved out of the Starting Position and gently placed into a non-Scored position by the Team.
This rule is intended so Teams can fix damaged Robots or help get their Robots “out of trouble.” It is not intended for Teams to use as part of a strategy to gain an advantage during a Match, including via moving Game Objects per parts c and d above. If a Head Referee sees Teams strategically exploiting this rule, they may be Disqualified from said Match.
Per G10, as long as the Game Object was still in contact with a Robot, then it has not "left the field". Therefore, G17c can be utilized to return the Game Object to a non-Scored position.