I can't imagine this hasn't been asked, but I cannot seem to find any official ruling about this.
For example - Sanctum Santorum with no spells cards in discard.
I'm pretty sure I have the right answer (the card can still be drawn), based upon the below, but hoping for some guidance.
1. You've checked restrictions
- you are in Alter-Ego form
- I can't find a definition for "change the game", but I'm presuming drawing a card (even without shuffling a spell) does change the game, because of cards like skilled investigator where the only resolution is drawing a card.
2. You can pay the cost
3. You've applied any modifiers
4. You pay the cost , which is just exhausting the Sanctum
5. There are no choose decisions
6. "The effects of the ability attempt to initiate"
- I think while writing this question I may have found the answer, but not directly. Given the way that "then" is specifically defined in the rules reference p. 17, I'm going to presume that the inverse is that resolution of effects (effects only, not costs or conditions), in the absence of the "then" modifier, can continue resolving unless they violate some other resolution rule. So as an alternative example, Iron Fist could could still deal one damage to an enemy even if that enemy were already stunned.
- I've seen other FAQ explanation where Caleb Grace has used the term "fizzle", which is why I have this question about how "and" is applied when resolving effects. I don't believe that is an official term, so I'm just sort of piecing together what I know based upon other FAQ's.
7. I don't see any reason why the the ability would be "canceled" in step 6.
- The triggering condition remains true
- The resolution of the effect is not a play restriction (i'm presuming that only way this would happen is either 1. before exhausting the sanctum an interrupt exhausted or removed it, thus you can't complete the cost payment in step 4, or 2. an interrupt flips you to hero form after you declare but before you complete checking restrictions.