I think the 'high stakes' are financial as in them continuing to live like superstars with private jets and £15 million mansions. Not only that, Meghan wants a 'voice'. Her obvious ego could not cope with a life in obscurity. No one would dance in the streets at the mention of her name!
They have nothing to offer aside from being royals and they didn't want to put the work into that (making inane chit chat with the plebs on a rainy day in Romford while cutting the ribbon on a new biscuit factory) or follow the rules of a centuries old institution.
Meghan may have got a few higher level acting gigs on the back of her being married to a prince, but at her age and with her level of acting, she certainly wouldn't have got to Oscar winning level and couldn't command the money actual Hollywood actors make. Harry doesn't seem to have the ability to hold down an actual job so when Diana's inheritance ran out, they'd be fucked. I assume he got an inheritance from the Queen but they didn't know how long she'd go on for, her mother lived to over 100, and had started all this before she died so couldn't back down as contracts were signed. I wonder if that's why they wanted to tone it down after her death?
They could could have easily used the vast amount of money they already had to live privately in the US within their means out of the public eye and would soon have been forgotten about.
I'm sure Charles would have seen them alright if they were a bit short on the kids school fees. I don't think he'd have cut them off financially if they hadn't started their all out war?
If they were really concerned about their safety, why leave the protection of the RF and run off to a much less safer country with guns in abundance. They do realise if some one from the UK wanted to harm them, they could just get on a plane.