Even then, Parikshit would be the king.
Chandra deva wanted Varchas, his favorite son to be on earth for only 16 years as Abhimanyu, force his foes to retreat in battle, have the battle take place when Abhimanyu attains his 16th year, die in Chakravyuha, and also have one son who will continue almost extinct Bharata race through the son of Abhimanyu.
And he who was known as the mighty Varchas, the son of Soma, became Abhimanyu of wonderful deeds, the son of Arjuna. And before his incarnation, O king, the god Soma had said these words to the celestials, 'I cannot give (part with) my son. He is dearer to me than life itself. Let this be the compact and let it be not transgressed. The destruction of the Asuras on earth is the work of the celestials, and, therefore, it is our work as well. Let this Varchas, therefore, go thither, but let him not stay there long. Nara, whose companion is Narayana, will be born as Indra's son and indeed, will be known as Arjuna, the mighty son of Pandu. This boy of mine shall be his son and become a mighty car-warrior in his boyhood. And let him, ye best of immortals, stay on earth for sixteen years. And when he attaineth to his sixteenth year, the battle shall take place in which all who are born of your portions shall achieve the destruction of mighty warriors. But a certain encounter shall take place without both Nara and Narayana (taking any part in it). And, indeed, your portions, ye celestials, shall fight, having made that disposition of the forces which is known by the name of the Chakra-vyuha. And my son shall compel all foes to retreat before him. The boy of mighty arms having penetrated the impenetrable array, shall range within it fearlessly and send a fourth part of the hostile force, in course of half a day, unto the regions of the king of the dead. Then when numberless heroes and mighty car-warriors will return to the charge towards the close of the day, my boy of mighty arms, shall reappear before me. And he shall beget one heroic son in his line, who shall continue the almost extinct Bharata race.' Hearing these words of Soma, the dwellers in heaven replied, 'So be it.' And then all together applauded and worshipped (Soma) the king of stars. Thus, O king, have I recited to thee the (particulars of the) birth of thy father's father.
Vaisampayana narrated the story of Abhimanyu to Janamejaya during the Sarpa Satra and he said father's father because Abhimanyu is the grandfather of Janamejaya.
So even though if Ghatotkach was alive, the almost extinct Bharata race would continue through Abhimanyu's son only which is why Krishna revived Parikshit even after Ashwathama released his brahmashira astra on Parikshit and killed him.
The thing is Chandra wanted his son Varchas to be incarnated as Abhimanyu and have Abhimanyu's son continue the almost extinct race of Bharata for which, the gods agreed.