What happens if The Grand Calcutron leaves the battlefield after players hand cards have already become programs?

Question

When The Grand Calcutron enters the battlefield, each player's hand becomes a program (an ordered row of revealed cards).

Players can only play the first card of their program.

If a card would be put into a player's hand from anywhere, that player reveals it and places it anywhere within his or her program instead.

At the beginning of each player's end step, if that player's program has fewer then five cards, he or she draws cards equal to the difference.

Assuming The Grand Calcutron enters the battlefield, it's first ability triggers and eventually resolves, and later in the game, it leaves the battlefield again - what happens to the cards in a player's program? Where will cards be put from this moment forward that would be put in a player's hand? Are there any other special interactions?

Answer 1

Mark Rosewater, the Un-set rules manager, has answered this question directly:

What happens to a program without the Grand Calcutron? Does it returns to hand? Can I play cards from it? Do I still need to follow the order?

If The Grand Calcutron every leaves play, the cards in the program return to your hand.

Answer 2

When The Grand Calcutron leaves the battlefield, whatever cards you had in your hand at that exact moment remain a program until you play them, any new cards you draw will be hidden (like normal), and you are no longer obligated to play only the first card.

The continuous effect created by The Grand Calcutron's first triggered ability is independent of Calcutron itself (CR 112.7a). It also has no stated expiration date. Therefore, any cards you had in your hand remain revealed and ordered indefinitely. It doesn't matter much that they are ordered anymore (unless someone plays another Calcutron), but they are ordered nonetheless.

112.7a Once activated or triggered, an ability exists on the stack independently of its source. [...]

However, The Grand Calcutron's second ability is a static ability. Static abilities only apply while the object they are printed on remains on the battlefield.

112.3d Static abilities are written as statements. They’re simply true. Static abilities create continuous effects which are active while the permanent with the ability is on the battlefield and has the ability, or while the object with the ability is in the appropriate zone. [...]

Therefore, when Calcultron leaves the battlefield, you can play any card in your program (as opposed to only the first card). Any new cards you draw will not be revealed, because Calcutron's second ability isn't around to make them part of the program.

The third and fourth abilities won't trigger any longer, because they are triggered abilities.

Answer 3

Superseding my previous answer, and due to the lack of detail and accuracy in the post quoted by this answer, I decided to rewrite it and hopefully clarify the exact functionings of this card.

What is a program?

A "program" is not much more than a descriptor for a hand revealed with The Grand Calcutron. As stated by the release notes (a.k.a. Unstable FAQAWASLFAQPAFTIDAWABIAJTBT):

Your program is still your hand, [...]

So what happens when The Grand Calcutron leaves the battlefield?

The release notes further mention something that isn't reflected on the card itself:

[If The Grand Calcutron leaves the battlefield,] the players pick their cards up and put them back in their hand. They are no longer public and no longer have to follow the rules of The Grand Calcutron.

A lot of technical details and interactions past this one are rather ambiguous, but in general, everything that interacts with a hand interacts with programs as well, in the same manner.

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What if The Grand Calcutron is destroyed in response to it's last ability?

The ability itself is independent of the source and will resolve as normal.

When Grand Calcutron was still on the battlefield, those cards would be put in the program and revealed in the process, but now they're just drawn as normal and won't be visible to the other players.

Are there any even weirder interactions? How should they be handled?

There are a few weird interactions that happen if you look at the exact ways the rules work, and the way The Grand Calcutron is templated. For example, if you counter the first ability, players won't have programs and therefore would be prevented from casting anything.

In that kind of situation, assuming this wasn't deliberately done because it fit one player's strategy, you should probably go with common sense over rules and ignore everything but Grand Calcutron's fourth ability. As suggested by doppelgreener:

With the Un-iverse intention that "The point of Unstable is to lean towards the fun side of the spectrum", the idea probably would be: if your hands don't actually become programs, then you just use your hand as normal. The abilities on [The Grand Calcutron] apply to how we use our programs, not how we use our hands.

As with everything else in Un-sets, it's probably best to solve problems like this within your playgroup.