I became pregnant after my husband had a vasectomy. Post- op 2 years. He had the test 3 months post op and the result was negative. Two years later I became pregnant ( by him) and he went for the test again and the result was 0 sperm seen. Either the lab messed up or there is more contraversery about vasectomies than we are aware of. Yes, a DNA was done and yes we went through hell and back. Well, allmost back.
In my opinion, the likelihood of pregnancy is extremely remote. However, given your age (42), my guess would be that the missed period may be connected with biological/ hormonal changes associated with Peri-Menopause.
At 42, it could be a perimenopause symptom. It's not so likely for you to get spontaneously pregnant as it was at, say, 22. Perimenopause can go on for 10 years, and the average American woman goes through menopause at around 52, so it wouldn't be entirely surprising. That said, was your husband tested after his vasectomy to be sure his sperm count was 0? If you find you are pregnant, and there is no other explanation but your husband, insist he go in for another sperm count so you won't have to defend against a bunch of suspicion from him.