Vasectomy Failed

We have 6 beautiful kids. He had 3 I had 2 and we have one together When our youngest was born I got the Mirena and soon after he got a vasectomy. This was 5 years ago. It’s time for my mirena to come out so he went and got retested just to be on the safe side and found out he is no longer 100% sterile. He has developed micro canals that sperm can and do get through. The dr says his count is low and it’s low motility. I’m getting my Medina out on nov 9 and we are considering “not stopping it” from happening. Do you think there’s actually a chance we could get pregnant? We both started a vitamin me prenatal and him preconception just so that if we do it’s got a healthy start. Thoughts? Are we nuts? Or could this actually happen?