I would not have had my child with “mild” ASD go on an overseas trip at that age unless I was one of the chaperones. But I know lots of kids with ASD, and for some of them it would be totally fine.
Some kids with ASD are… I guess you would say different outwardly, or present in an atypical manner. However, they have perfectly reasonable coping skills and ability to manage unfamiliar situations.
My son is extremely anxious in unfamiliar situations, and struggles with unexpected changes to plans. He also has poor emotional regulation. That means if he gets upset, he might have a “meltdown“ (which for him have never been violent, but more like a crying, emotional storm that you might expect from a much younger child). But I know other kids with ASD who actually don’t struggle with unfamiliar situations or changes to plans much at all, and have relatively good emotional regulation. Maybe those kids have more sensory challenges, and have ways to manage them.
I would trust the school to be familiar with the child, and help the parents decide if the trip was a good fit for him. I could also see a situation where a family might not think the trip was a good idea, but they would like their child to come to that conclusion on his own. We have done that often with our son. We think a particular event might be beyond what he can handle, even as a stretch, but part of the process of growing is getting information and thinking through what it would be like for him, and whether it might be a challenge that would be positive.
For instance, my son wanted to be in a musical when he was in middle school. We had a feeling the disorganization of practices, and uncertainty surrounding what would be done each day, and the required flexibility would be a little more than he was able to handle at that point. However, it didn’t feel right to tell him he could not do it. And it was fairly low risk. So we discussed with him what it might be like and what some of the challenges were, and how he might deal with them. He also talked to the people running the program. In the end, he went to the first two practices, and then decided it was too stressful. But the process of getting information and deciding on his own was more independence building and encouraged more growth than if we had just told him we didn’t think it was a good idea.