We sometimes joke that we can spend $$ when we get a discount or make a return - like "We saved $20 on that shirt, now we can spend $20 on something else! ha ha" - But we'd never do it. So, A is completely out. Just becuase we decided to splurge on A, doesn't mean we go find something else to buy when we didn't get it.
In general, we always do B with our money. We pay off our CC at the end of the month, even in December. I would be beyond relieved if a $750 splurge didn't go through if I couldn't pay-off my practical bills/CCs.
I would go with B or C but I know my H would opt for A. Once it's "spent" it's gone and accounted for in his mind so if he wasn't getting toy X he'd want to find a toy Z.
Until you said MacBook, I was thinking this was an awesome pair of shoes. If it had been shoes, I'd have gone and bought another pair, or waited until you found another awesome pair you loved and bought those. Totally not MM, but that's my honest answer.
If you can afford it, the money's already been spent. If you want it to be a splurge for both of you, maybe save it and earmark it for a vacation? Or 2 nights for weekend away in a nice hotel?