Say someone dies abroad, in most cases the family would want to bury/cremate that person in the country of origin and the cost would be covered by insurance or themselves. But assuming repatriation is not a requirement for any relatives/friends, is there any international law saying the body should be repatriated to the country of origin? Or are there many countries that have laws concerning this?
No, there's no such requirement, the family can choose to either repatriate or bury/cremate locally. Assuming nobody claims the body, local authorities will give the local equivalent of a pauper's funeral and the remains will stay in that country.