Sorry have no first experience but I do know someone whose wife died and his visa was not renewed as he was technically not married any more. Seems very harsh. Maybe just do retirement visa.
ah ok well Qatar airways accepted when I left London. And immigration asked and accepted when I arrived in Bangkok but it's always down to the official you see so luck of the draw
In my experience easy,fast and cheap are not words that you can use when it comes to getting a visa for a girlfriend to visit the UK and in guessing USA is the same