In a way it starts off as a 'game', but in the cold light of day, your wife is engaging in sexual reproduction with another man, with your approval. You then can't say too much if the end result of this is pregnancy, as it was you (the husband) who initiated this mating process. I think you need to allow her to have the baby, really the decision was made when you started this off by interesting her in BBC you just have to stick with it and see it through. Additionally if she becomes pregnant, you shoould spend an amount of time thinking about what you have done, and why. I'd think also it would be a good feeling.