He would have probably shed a few tears unseen, then picked himself up and cast Kotoamatsukami on Obito, ordering him to kill everybody in Akatsuki or die in the attempt, killed Deidara for daring to touch one hair on his brother's head, given Naruto or Kakashi all the info he had on Akatsuki, reveal the inner workings of Akatsuki and the secrets Pain and Obito kept to the other members, thereby inciting strife, then watch the organization collapse upon itself with his eyes filled with mournful tears for his brother.
Then, marry some chick and create a new Uchiha clan under peaceful ideas and without bloodshed.