Massive? No. Assuming their Apple devices didn't also suddenly stop existing, they'd have a little pain with transitioning to alternatives. There are plenty of alternatives out there to Apple products right now, and with Apple corporation suddenly winked out of existence, that'd leave a big gap for other competitors to take over that space. If anyone is completely and utterly dependent on Apple for their livelihood, that's really their own dumb fault. Nothing apple does is all that critical that you can't get something/someone else to do it, though of course there'd be some pain in the transition. (The same goes for anyone willingly locking themselves into any proprietary vendor.)

I guess one drawback is that we'd probably see a significant uptake in Windows Phones, and they might actually get above 5% marketshare....

Anyway, MS bashing aside, my point is: Apple is just a seller of convenience, nothing they make is all that critical that it can't be replaced. Anything you can do with an iPhone, you can do with an Android phone. Anything you can do with a Mac, you can do with a Windows or Linux PC. It'd be annoying to have to get a replacement device and migrate to it and maybe new software, but "massive negative impact"? No.

Now, if everyone's Apple device suddenly winked out of existence too, that would be a bigger problem, but that's because of the data stored on those devices, not because of the devices themselves being so valuable. But as long as they kept backups of anything important (and not on Apple-branded backup devices...), that shouldn't be that hard to work around either.

I'll also add that it's not that much different for MS. If they suddenly winked out of existence, it'd be a pain, but "massive negative impact", not that much. There are alternatives, and it'd force everyone to have to explore those alternatives finally. It'd be a much bigger problem than Apple winking out of existence, however, because of MS's strong position in business software.

Of course, part of this depends on whether MS's software also winks out of existence, or if only the corporation itself gets swallowed up in a space-time continuum rift. If the software stays, it wouldn't be much of a problem at all: people would just continue using MS-ware as they currently do. A lot of people use illegitimate MS software anyway, so no change for them. Corporations would have less hassle with licensing. The main problem would be security updates, but that's been screwed up lately anyway because MS has been using that to force unwanted updates and ad-ware and spyware.