I'm assuming that a page has a life, I picked five years. The implication being if your page isn't going to last long, it's not that big a deal if you rely on an external resource. But if you're one of the few (or the many) that are going to last longer than the expected life of one of these ephemeral services, you shouldn't rely on it. That's as opposed to paying for the services of, say, an established, paid and hopefully long lived CDN or similar.