[a3n]

> Most importantly, the team that developed it has moved on to other work and it hasn't been restaffed.

Isn't that right there an example, or warning, or admonition, or something, suggesting that you not use external services for essential features? I know that no page is likely to last more than five years, but there are going to be many pages that outlast services like this.

Or am I missing the target use case?

[SiVal]

I'm not quite sure what you mean by "no page is likely to last more than five years," because a large portion of the Web is composed of pages that, once posted, remain indefinitely. If your site is one of them, you wouldn't want to depend on an external source for your charts, or your archived pages could be broken by a third party--which seems to be your (very good) point, so I'm a bit confused by your wording.

[a3n]

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.