> and they would have plenty of time to course-correct
Not in the common scenario where they have married and had children abroad.
I do know of some people who left their country for 10+ years and returned. In all cases they had married somebody of the same nationality as theirs and moved while the children were still too young to care.
In other words, the people who can easily return typically do so. Those who don't return often want but can't for one reason or another (usually their new family).
If they gave it a go and it didn't work out, then they know, and they would have plenty of time to course-correct. There wouldn't be any doubt.