The possibility is present, when news of the revolution in Portugal first reached Brazil, the King initially planned to send Dom Pedro to Portugal and have himself remain in Brazil, and he published a decree on 18 February 1821 whereby Dom Pedro, the Prince of Brazil would return to Portugal. The Cortes in Lisbon had already demanded the return of the sovereign on 26 January 1821, therefore on 7 March 1821 the King decided that he would indeed return to Portugal to promulgate a constitution. The royal family reluctantly left Rio de Janeiro on 24 April 1821, arriving in Lisbon on 3 July of the same year. With such a long voyage, the possibility of a storm or some other disaster could sink the ship.
According to the laws of succession, Pedro automatically becomes King Pedro IV of Portugal, Brazil and the Algarves. If he refuses to leave Brazil, what might ensue is a sort of junta governing Portugal, with allegiance to the king in name only similar to what happened in the Spanish colonies in the Americas. France had intervened in Spain to restore absolutism in 1823, perhaps something of the sort could occur in Portugal.