Nuon Chea collapsed in his cell at the tribunal detention center outside Phnom Penh on Sunday, Son Arun, his lawyer, said.
An annual meeting of the Mekong River Commission, which includes representatives of Cambodia, Laos, Thailand and Vietnam will be held in Laos on Jan. 17.
The six sailors dropped their official complaints after a reported compensation offer of $20,000, but the criminal case continues regardless, court officials said.