Actually since a pack is 100 and arena entry is 150 if you don't get 50 gold you're losing gold.
Yyyyes, Like I said the pack pays MOST of the gold off. Not all of it.
What I mean is you're not really wasting it because you're still getting most of the gold back in form of the pack, and what you don't is pretty much paid as fee for the chance to get more gold back- In sense, it's not wasted because you paid for the opportunity cost.
Not to mention even going 0-3 you're still getting experience for characters, so even if it's a sharp cost you're still getting more than the pack. Oh and the second box besides the pack has some dust or something.
So basically even if you 'lose' the 50 gold you make it up anyway through experience, opportunity cost, and the shinies pretty easily :v