What you have here is the problem of not really owning the content if you want to do what you are doing. Apple doesn't own this content, the studios own it. And they can stock or unstock the iTunes store as they wish. When the movie is available, you can stream it. When they take the movie out of the store, it's lost.
We don't own iTunes-purchased content at all (instead it's "lifetime license" at best). And if we don't download and store our purchases so that we have no dependency on iCloud, we can lose them at any time.
Buy the BD or DVD and actually own your media in a very full way. Rip it and store it in iTunes just like you ripped your CDs. This gets you almost all of the benefits & niceties of iTunes media management without the whims of the Studios or Apple affecting your perception of ownership. And instead of a "lifetime license" (where others get to decide what lifetime actually means), you actually own it such that you could sell it, will it, or give it away to someone else who could then fully own it too. If it's BD, you also get to decide the quality of the video (rather than the Studio or Apple deciding it for you) and can optionally enjoy a far superior audio track vs. 1992's Dolby Digital standard.
Yes, ripping is a hassle and storage has some cost but trusting a big corporation as caretaker of your media and that caretaker being entirely dependent on what their suppliers of that media want to provide- or take away- is begging for vanishing media and other anti-consumer surprises. iCloud is not the end-all, be-all answer... it's just one option. And a mentality of "stream everything from iCloud" is only music to the ears of those who sell (and increasingly pinch) bandwidth tiers... companies like AT&T, Verizon, Sprint, Comcast, Time Warner, etc.
