Until someone removes their profile, and everything you share with them is lost to the aether. This is the reason I think Google chose to keep all posts in your stream, so even if those people delete their profiles, you still have the content you shared with them. Because it's your content.
It's a software function, actually. If it were hardware, we'd need new iPhones and iPads to use it. But that's just arguing semantics.
And you can never be too sure what Apple will and will not agree to. After all, iCloud is primarily a service to sync devices together; access to the uploaded content in the cloud was a brief "oh yeah, BTW" footnote. Until Apple has a social media service, Google offers functions that are completely not present in their ecosystem.
They may also decide to integrate G+ like they did with Twitter, to keep pace with Android's ability to do so and, well, to stick it to Facebook as payback for Facebook trying to flex its muscles against Apple.
Google and Apple have a mutual enemy in Facebook, a company that thinks that it owns not only their users' content, but by locking in its users, thinks it owns the internet as a whole. No one wants that, ESPECIALLY Apple and Google.
Look at it this way... G+ integrated into iOS, Ping integrated into G+... win-win.