The Mexican tenor, “who cancelled all his 2009 engagements after a cyst was found on his vocal cords, will make his comeback” at the Vienna State Opera in “a one-off appearance in Donizetti’s L’elisir d’amore on March 22. … [He] is then scheduled to sing the role of Lensky in Tchaikovsky’s Eugene Onegin at the Berlin State Opera on March 26 and 31 and April 2.”