Bashir flew out of South Africa earlier today, dodging a court order for him to stay as local judges weighed up whether he should be arrested over alleged war crimes and genocide.
The ICC was "disappointed that he was not arrested. Our position has always been that South Africa's obligation is clear and unequivocal. It had an obligation to arrest him," the court's chief deputy prosecutor James Stewart told AFP.
South Africa is a signatory of the ICC, which has often been criticised for only targeting Africa leaders.
At the summit, Bashir attended a group photograph on Sunday along with South African host President Jacob Zuma and Zimbabwe's President Robert Mugabe, who is the chair of the 54-member group.
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Today was the final day of the summit.
Sudan officials in Johannesburg had earlier brushed off the court case and said the South African government had given them assurances about Bashir's trip before the summit.
The fact that Bashir had left before the summit ended showed "that ICC arrest warrants actually means something."
He said the prosecutor's office could now ask ICC judges for a referral to the UN Security Council over South Africa's failure to comply, but that "we'll first let everybody catch their breaths."
Stewart added: "This is a long game and patience ultimately will pay off.