Thanks for your query.Based on the facts that you have posted it appears that you had your vasectomy
35 years back and you have sexual relationship with your partner .You are suspecting your partner to be pregnant as period is delayed just by 3 days.
There are no chances of failure of vasectomy after 35 years at all as anti sperm antibodies
are formed in your body..Her period may be delayed due to hormonal
imbalance which happens many a time in some females.So do not worry at all..