Generally, if a joint petition for divorce has been filed then both spouses must sign the paperwork, according to LegalZoom. If one spouse refuses to sign, or is not available to sign, the party that filed the joint petition can opt to file a regular divorce petition, which does not need the signature of the other spouse.
DivorceNet notes that judges may use their discretion and allow a joint petition to proceed through the process, even without the other spouse's signature. In this case, it would be treated as if it were an uncontested divorce, which are considered to be the easiest route to a smooth settlement. Normally, uncontested means that both spouses have agreed to divorce terms related to custody, finances, property and support issues.
DivorceNet also notes that after serving a spouse with a divorce petition they have 30 days to respond. If they should fail to respond, a person may file a default request and judgment proposal with the court. A hearing is set and both parties must attend. Should the other spouse fail to appear at the hearing, they lose their right to have a say in the divorce proceedings. A divorce and judgement could be issued under these circumstances.