This is so beginning to read like a rerun of Edward VIII and Mrs Simpson, even though Prince Harry is a long way down the succession list.
The choices ahead of them seem to be a pointless exile and useless life in a foreign country, like Edward VIII and wife in France, in fact I think this is what -will- happen to Harry, there is no other option. Edward VIII also saw himself as continuing to be able to represent the crown in various ways after his abdication. They did make him Governor of Barbados, but only to get him away from his Nazi chums during the war, otherwise he might have been interned, but otherwise he was right out of it.
If the marriage fails Meghan will end up like Fergy, a member of the demi-mondaine, wandering around the edges of society in the US, trying to get some money where she can and struggling to stay solvent as her interest to the public wanes. She will probably ending up like her father, a beached hulk, of interest to no-one.
All rather sad.