In case Charles dies before Camilla, I believe he will leave her very comfortably off as he has amassed quite a personal fortune over the years, so can provide for her in the style he has made her acustomed to as his wife. I say this because I don't think Camilla personally needs that luxurious life she lives due to her husband's wishes and their position in life.
Probably she will acquire a suitable residence in London which she will maybe share with her son and his family. As Tom Parker Bowles is a scion of the Parker of Macclesfield-family, I guess it won't take long till the queen or the new king will create him a Knight Commander of the Royal Victorian Order for his services for Camilla - thus creating him "Sir Thomas" Parker Bowles. Which would be entirely suitable for the son of a Royal Lady who takes care of her in service for the souverain.
I personally can see Camilla being as interested in and charming with Charles' grandchildren as she is with her own, thus she probably will become the Royal "Granny" - a somewhat retired and no more really prominent Royal personality, but still present and upholding an image as the kind and loving Dowager of the RF.