When semen touches air sperm die? & can they come back to life if moistured?

Be careful! Sperm do not live long outside a proper environment. If all the semen is dried and there is no moisture, one can fairly well assume that all spermatozoa are dead. They are not "freeze dried" or dehydrated and spring to life with bit of water, etc. However, i wouldn't take any chances if pregnancy is not intended. Practice responsible and safe sex. Categorically----no!