A few things:

1. You don't say what kind of miles you used to book these tickets. It matters because different airlines have different policies as to how lap infants are priced, and I believe it goes by the policies of the booking carrier, not the one actually transporting you. The difference between 10% of the adult fare at the time of booking v. 10% of full fare is significant, and it depends on the airline (and perhaps, the agent) which one you'll get charged. Also, I'm not sure if you can book a lap infant until the child is actually born, so presumably fares could be higher by then.

2a. 2 months after giving birth is fairly close. If the baby is late, it might be only 6 weeks post postpartum. If your wife has complications, it may not be comfortable for her to fly.

2b. 2 months is when the first major round of vaccinations is normally given, although my pediatrician told me that they can be given as early as 6 weeks. Just an FYI and something to consider.

3. If I were going to try this, I would ONLY do it with a 100% breastfed baby. The logistics of trying to manage bottles & formula water, etc, on a long haul flight give me a headache just thinking about it. Yes, it's possible, but I would only do it if it were a NEED.