A conceit, an ironic barb, wit can be searing and funny. In the case of Margaret Edson’s Wit, the Tony winning play now in a Manhattan Theatre Club revival at the Samuel J. Friedman Theatre under the fine direction of Lynne Meadow, Wit follows the journey of Vivian Bearing, a name that loosely translates to “enduring life,” a college professor specializing in 17th century metaphysical poetry, in the verse of John Donne to be specific, author of “Death Be Not Proud.” As performed by Sex & the City’s Cynthia Nixon, she is a brainy Everyman/woman, precious in what she knows and does, vital in knowledge, commitment, and contribution to life, devastating to lose. And lose her we do. Sorry for the spoiler: she dies at Wit’s end.