It is perhaps sign of these pandemic times that several Off-Broadway plays opening in the coming weeks all deal with severe illness. Manhattan Theater Club will stage Martyna Majok’s Cost of Living, featuring a character with cerebral palsy. At the Atlantic, Gracie Gardner’s I’m Revolting is set in a skin-cancer clinic, and next month the Roundabout offers a work by Noah Diaz with the on-the-nose title, You Will Get Sick. But first, the Yonder Window Theatre Company gives us Jasper, a thought-provoking drama in which a boy with a fatal illness tests the limits of his caring parents.