Forgotten pacts

[Maveric78f]

My opponent plays a pact (slaughter pact for instance). Then, he forgets to pay the upkeep. I know that he used to lose the game, but I've met several people that say that this ruling has changed (it's somehow an obligatory action now) but are unable to prove it with any official ruling.

Is it bullshit?

[luma]

The paying has always been "an obligatory action" in the sense, that if you have enough mana in your mana pool, you must pay the cost. You don't have to tap your lands for mana, though, so this way the paying can be seen as "optional".

If the trigger is forgotten, this is what IPG tells us:

If the trigger has an instruction that specifies a default action associated with a choice made by the controller of the trigger (usually "If you don't ... " or "... unless") resolve the default action immediately without using the stack.

So, because there is a default action ("You lose the game"), that action is instantly resolved and the player loses the game (and gets a caution/warning for missed trigger).

[Maveric78f]

How is it obligatory if I have mana in pool. Let's say there is a Tabernacle in play and I have Gaea's Cradle in play. I have Genesis in graveyard, so that I use my cradle to resurrect 1 creature. Then I forget to pay for Tabernacle. As I had some mana left from Gaea's Cradle in pool, do I only have to destroy 3 of my creatures?

Edit: Ok, I got it. Pact says "pay 2B, if you don't, you lose the game". And not "you may pay 2B, if you don't ...". The Tabernacle say "destroy this creature unless you pay {1}", so the creatures get destroyed even if you had mana in pool.

[luma]

Right. "At the beginning of your upkeep, destroy ~ unless you pay 1" is the same as "At the beginning of your upkeep, you may pay 1. If you don't, destroy ~". The pacts don't have "may" in the ability, so the paying is mandatory if you have enough mana in your mana pool.