Tony winner Stephanie J. Block and Broadway-alum hubby Sebastian Arcelus were supposed to appear on the one-night-only return of The Rosie O'Donnell Show in support of The Actors Fund, but duty called to be parents. (If you're wont for a couple's duo on Rosie, Audra McDonald and Will Swenson did sing an acoustic version of "Smile.") Regretful that they had to miss out on the fun, Block and Arcelus took to …