It is unlikely that paid relays for real can guarantee that they will not close after some time and the data stored on them will not disappear. I generally have a hard time understanding why paid relays might be needed if everyone (including OGs) complains about spam from time to time and content selection and filtering is available at the client level. There's no killer feature of paid relays imo. And for some reason I think that free relays that copy content from other relays, if they are rotated in a timely manner, can be even more long-term storage for your content than paid relays that risk closing due to low profitability.