On Stage and Off column; The Coast of Utopia, Tom Stoppard’s nine-hour, three-part epic about love and revolution in 19th-century Russia, will come to Vivian Beaumont Theater from Royal National Theater in London with new director, Jack O’Brien; show De La Guardia to close after nearly five years at Daryl Roth Theater on Union Square; Tony and Tina’s Wedding, second-longest-running show in Off Broadway history, will also close in May; show opened in 1988 outside church on Christopher Street; Denny Doherty, only surviving Papa of Mamas and Papas, plans musical California Dreamin’ recalling stories and songs of band; photo; Jared Harris, son of late actor Richard Harris, to star in American premiere of Humble Boy at Manhattan Theater Club; play was hit at National Theater in London (M)