Maurer was a spineless weasel. He wouldn't take the top posting, he always styled himself as a schemer.
Grandad was firmly convinced Apostol was to have been Dej's successor, had it not been for Maurer's insistence to dump the Dej branch of the party.
A dark horse would've been Corneliu Mănescu, the Minister of Foreign Affairs. Though he might've been susceptible to accusations of 'Westernism' by the hardliners. Another potential candidate was Alexandru Bârlădeanu, Minister of National Economy and president of the Central Planning Committee, though his open anti-Soviet stance would've clashed with the Soviet Union's agents inside the Communist Party of Romania.
Gheorghe Gaston Marin had a lot of influence inside the Party (was the last of Dej's inner circle to be removed by Ceaușescu), but he, like Silviu Brucan, was Jewish. Romanians didn't suddenly stop being latently antisemitic after the arrival of Communism.