One way to frame the topic, is to point out he doesn't owe birthday-person, he owes you - so his non-appearance at the party doesn't do anything for you, it doesn't balance the debt owed.
He's not owing money because of the birthday person or the party or even the present, he owes it because he opened his mouth and said he would pay you back - very specifically, he had the option to say no, and did not. He had the option of letting you know his willingness to chip in for the gift was dependent on his attendance at the party (why?!), which might have let you know to pick a different gift, or have people chip in the rest, or pay the rest without the deception, whatever you would choose if you knew you were going to be short by that amount.
Even letting you know he decided he didn't want to pay you back, when he decided to skip the party (and not afterwards) would have been more honorable, since it would involve him standing by his decision and willing to endure awkward conversation for his greed. Though, yanno, not much more honorable, since he was still stiffing someone who had nothing to do with his decisions.
If he had bought the present himself, he would have a very hard time arguing with the store or credit card that he should get the money back (and keep the item, since it was already gifted) just because he "didn't go to the party". He chose to owe a debt instead of paying upfront or opting out, the debt doesn't vanish just because circumstances (actually unrelated to that debt) changed.
The actual debt, well, it may be just the cost of the lesson that he is not trustworthy - and it might be easier to write it off. Especially if you are willing to write him off, which I would be. There's usually little benefit to dealing with someone who won't hold by their own word, won't deal with their own decisions - and I would not suggest you maintain ties without making your point clear, or it will likely lead to further shenanigans.
This framework may still be useful, though, if you wanted to confront him, if you wanted to keep friendly(ish) connection with him for some reason.