That’s 100% dependent on why you went no contact in the first place. It doesn’t sound like you owe him anything, so your only question is how it relates to your own feelings.
If your ex brother in law has both your and his contact info, it sounds like he could’ve reached out indirectly at any point.
You don’t have time to have a kid before this surgery if it’s in January, and I don’t think either of you want this stress.
Best cast scenario, it’s not cancer, move forward however.
Worst case, you have to decide between terminating the pregnancy or removing the cancer.
And the inability to have biological children does not preclude you from becoming parents. Yes, it’s a much more complicated process to adopt/deal with surrogacy/etc. , but you’re not completely cutting off the option to raise a new generation.