My 40 yr old wife is pregnant w #2 (7mos) & developing severe vericose veins. Her obgyn isnt concerned but shes afraid they wont go away after babys born?

Right to be worried. Pregnancy is the #2 cause of varicose veins, and the effects tend to be cumulative with each gestation. Although the veins may decompress and seem to disappear with delivery, the underlying damage to the veins remains, and will likely progress in the future. She needs compression stockings now, and definitive treatment post-delivery. If severe, she can be treated now, as it's done via local anesth.
They probably won't. Varicosities, like weak spots on a balloon, never truly go away, although a decrease in pregnancy-caused pressure with birth will certainly help to make them less pronounced. For now, get her tight elastic stockings - not necessarily stylish but may be considerably more comfortable..
:( First off congrats to you and your wife on the pregnancy! unfortunately, they do crop up as women age; and can be exacebated by pregnancy. After delivery they may subside but sometimes they persist. Fortunately there are plenty of treatment options for them so tell your wife not to despair; concentrate of the pregnancy. Again, congratulations!
Veins. Varicose veins during pregnancy are common. The best thing to treat them with during the pregnancy is compression stockings 20 - 30 mm compression. I would recommend thigh high and have her were them until 2 weeks after the baby is born. She can take them off at night to give her legs a break.