Not everybody is perfect and not everybody would tolerate such a mistake from their spouse to be. It is quite unfortunate that this should happen, he might be seeing it as a kind of wanting to see or exploiting means of doubling their savings to surprise his girlfriend but it went south that he lost everything. I was curious as to know if it was his first time of gambling or the possibility of him being convinced by friends or so to try do such hoping that he could win the game and double the money for their marriage. If he is a gambler, that should have been detected by his girlfriend long enough to have known what to do before then and she could have opted to save her money separately than putting it together with him.
Is a good question it would have been nice to really no his record in gambling and if it was his first time of gambling, so if it was his first time then his intention may not be as bad as we are looking at it and like you said it could be the handwork of his friends who knows, actually the more I'm seeing different opinion of members that's how I'm seeing the reason why the two of them needs to patch things up to continue their relationship even if the money is very big for them to save again but with time they would come up with something because if the woman leaves him means that she does not love him that much because a woman who knows that it was a mistake regardless of how furious she could be she would forgive and continue because even the marriage they are going into could still have difficult times so her judgement now will reflect to her tolerance in the marriage.
A very good contribution I must say, I do not know the two persons involved in this incident in person, and like you rightly said, there is no way to know if the man have been a gambler before the incident, or the incident was his first experience with gambling, there is absolutely no way to know, but one thing I am very sure of was that, whether or not it was his first time gambling, his intentions were pure as I believe many of us can see or feel, he had good intentions and only wanted to try to contribute to their wedding since it has been his wife-to-be who has been working and gathering all the money.
But his only and very stupid mistake was using all the money to gamble as he said he was trying to double it, its unfortunate though, and must be very painful for the woman to forgive, and to be honest with you, marriage is not just about both parties loving each other, love alone does not and will not keep a marriage.
So, after an incident like this, the only thing I think will make the woman still consider moving along with the man is simply the other good qualities the man possess, without any other good qualities for the woman to hold unto in the man, it will be hard for her to forgive him on the basis of love - remember the popular saying that "there is a thin line between love and hate".