Stephen Saito Carlos Marqués-Marcet brings life to a grave situation in “They Will Be Dust,” realizing that when so many tiptoe around the subject of death, it might not be such a stretch to put an elderly couple in ballet shoes if they’re thinking it’s time to choose for themselves to shuffle off their mortal coil. The unconventional drama proves moving in more ways than one when following the septuagenarian pair that has booked a one-way trip to Switzerland, achieving a level of intimacy unusual even for its reliably sensitive director when music and dance can crack open what mere dialogue cannot.