The government of Papua New Guinea will find out if it legally took power from Sir Michael Somare when the Supreme Court hands down its decision on the 9th of December.
The decision will follow months of legal wrangling over the August 2 election of Peter O'Neill, after 70 MPs decided to dump the Somare government.
The Supreme Court rose on Friday after two days of closing arguments.
The Chief Justice, Sir Salamo Injia, told the courtroom a panel of five judges will take the "whole month of November" to decide whether the dumping of Sir Michael was constitutional.
The lawyers for Sir Michael, former acting prime minister Sam Abal and the provincial government of Sir Michael's constituency, East Sepik, have argued no vacancy existed in the prime ministership when Mr O'Neill was elected.
Sir Michael had been in Singapore for four months recovering from these separate heart operations when the decision to oust him was taken.
In their arguments, government lawyers have said Sir Michael was incapacitated and could not do the job of prime minister, and that the decision to switch power was in the national interest.
