Harry I imagine did not intend to quit the royal family and leave the UK for good,
Biscuit - I actually think it's the opposite. M, who has come from modest means, probably couldn't believe her luck when she found herself being 'elevated' to the ranks of royalty. Evidence for this - her immediate 'showing off' of wealth and privilege, speaking badly to staff, wearing inappropriate clothing (e.g., the 10k ballgown to some Australian Geographical Society dinner where everyone else was in moderately-priced business suits or business dresses). This is absolutely not how wealthy people behave (the main reason being that if you draw attention to your wealth too much, it can be taken off you either by the authorities or by the ordinaries).
M is a victim of her own boundaries (just like everyone else), mainly to do with her lack of knowledge and of common-sense. She probably encouraged H to become an activist by kicking back against his family - too much. He got all fired up, took off, and she had no choice but to follow. I am beginning to see this more and more as a very public lesson in 'be careful what you wish for'. She is, quite possibly, horrified at what has happened. I have never observed anyone who has experienced upward social mobility to be happy about tumbling back down to their more usual place. Those who are saying that she willingly walked away are reading things incorrectly. I can almost guarantee that no-one would give up everything that she has given up for the sake of 'activism' or a political cause. Crikey - even Mother Theresa didn't.