Of the Sunrise students that I know that have completed year 9, most of them have gone onto other international schools and they have all done well. One student moved to a good school in Austria, where he ended up teaching English to his English teacher before winning a scholarship at a reputable arts school.
If students move to other countries, they usually just need to take their school reports with them. If they are going on to university, they may need to do a bridging course or some sort of test, but this would happen if anyone was going to school in another country.
Most of the international and national plus schools offer some sort or internationally recognised certificate.