See Section 18.2 of the Doctorate Regulations.
If a candidate has not submitted a thesis by the maximum approved end date, the candidature will lapse. A lapsed candidate will no longer be considered a student of Monash University and will not have student access to the facilities and resources at the University. The Graduate Research Committee (GRC) may allow a lapsed candidate to submit the thesis for examination any time within three calendar years of the lapse of his/her candidature. In order for the thesis to be accepted for examination, clear evidence of continued contact between the candidate and supervisor over the period of lapsed candidature and a certification by the main supervisor that the work meets the necessary submission requirements must be provided.
Applications to submit as a lapsed candidate, supported by the candidate's main supervisor and head of the academic unit or graduate coordinator, should be submitted on the Application to Submit Doctoral/Research Master's Thesis Under Lapse of Candidature Regulations Form (Monash only).
See also section10.1 of the Doctorate Regulations.
Where a doctoral candidate allows his/her candidature to lapse by failing to re-enrol, the candidate will not be readmitted within four years of the candidature lapsing, unless GRC considers that exceptional circumstances warrant an earlier readmission.