I would strongly recommend you join an expat forum like the one I recommended up thread eg twofatexpats
You will get replies on there that aren't anglocentric amd from people who have actually done this.
Looking at PISA data the number of countries who sit exams at age 16 is in the minority. You will find other countries (and as such then universities) don't give much/any emphasis on GCSEs. Its all about testing at age 18.
Even if your DCs come back to the UK for uni just remember universities take students from all around the world not just UK so are used to different education backgrounds. That includes having no GCSEs or just a few. Yes if you are British and gone through the UK for something like medicine they'll look at GCSEs as well but there is a world outside of the UK and unis know this!
Any good international school will be used to this scenario, they will have different pathways open to pupils who start at different times in the year and from different countries. There is usually a pre-sixth form route for pupils entering in y11, this is a condensed timetable of 5 GCSEs all they need to stepping stone into the next stage.
If your child is only going to miss a few months of y10 you could even ask if they could online school, this would cost you though.
Please take this the right way, once you leave UK chat rooms you'll find this isn't that unusual! People on the international circuit move all the time some with just a few weeks notice. A good international school won't bat an eyelid and have systems in place.
I would recommend you speak to the school to start with and see what they can offer in terms of support.
And to answer your question, yep the opportunities will be well worth it!