Great questions and I talk with couples on this topic daily.
Is your husband's sperm count and motility in normal range, 20 mil/ml or higher and 50% or higher? If not addressing the slightly low numbers would be the first step.
After a reversal (VR) it is possible to have restriction at the surgery site and this can be managed with anti-inflammatory medications. Another great option would be Clomid for him. Clomid will boost sperm production and sperm quality.
As hard as it is to have a miscarriage it is a positive sign that he has fertility and his sperm can get the job done. Why the pregnancy didn't stick is hard to say in terms of male or female caused.
I would recommend checking everything on the female side just to make sure hormones are in check, ultrasounds look good in terms or ovarian function and the uterus and fallopian tubes have no blockage. Sometimes going through some of those workups does the trick and couples will end up pregnant on their own.
Amy Perkins, MS, TS
Laboratory Supervisor
Arizona Andrology Laboratory & Cryobank
International Center for Vasectomy Reversal