I don't know why there has to be consequences. They had good reason to smash it and it was the smart thing to do given that apprentice was getting th' ol' crazy Saruman-eyes!
Of course if someone warns them not to press the big red button because of x consequence and they decide to ignore the warning and do it anyway, then go nuts. But punishing them for making a smart decision says "You're screwed no matter what choice you make".
I'll disagree for a couple reasons:
The outcome of any given action is not always known. Destroying ancient artifacts comes with great risk, which means a greater number of possible outcomes. If every decision was made with perfect knowledge, there really wouldn't be much point to making a decision because there's only be one real choice.
Sometimes you are just screwed, no matter which choice you make. Leave the relic alone? Drives wizard power crazy. Take relic? There's now a break in the circuit, crazy wizards hunt you down or the object just screams power in all directions attracting dangerous foes. Destroy the relic, the wizard goes mad with grief, the relic was his last hope to restore his petrified lover to life and spends the rest of his days hunting you down. Perhaps the gods become angry.
Or perhaps nothing happens at all.
All of these are perfectly viable options.
@OP: I'm a big fan of laying out some potential outcomes and then letting the dice decide. Pick your top 5 outcomes, roll a d6, on a 1, nothing happens, lucky them. If you want a better probability range, take a d20, remove the 20 and the 1 for either spectacular bad business and nothing at all, then spread the remaining options over the remaining numbers.
What the players should never have is perfect knowledge.