My two cents is no, don't say anything about it yet. If his answer is "I'm leaving and my plan is to send her a card on her birthday" he's saying that to YOU. And there's a lot of friction between you two now. If it is brought up after the birth (and *maybe* the BIL should approach it-- maybe even at WH's first meeting with the baby), he's saying it to HER. And that might make his answer different.
All I know is that with my WH, there's so much rebellion. It's like, he knows what he's doing when he's rebelling against somebody. When there's no one to push back against, he suddenly doesn't know what he's doing anymore. I sort of think of my job as clearing the way of people to push back against so he can truly act on his own.
I give this advice because it's what I would do if my WH and I had been in conflict right before the birth. But I completely understand if you feel that something different is better in your sitch.
