The most senior figure is Francesco Arcadi, who was already acting boss when Vito served his sentence in the US.
Arcadi was Vito's faithful Underboss for years and - as a Calabrian - was essential symbolically to keeping the Sicilians and Calabrians working together under the Rizzutos in those years. His brief tenure as acting boss however, was disastrous. He's a solid number two though and despite his lineage has always proven to be one hundred percent faithful to the Rizzutos.
The other name who is back out there, and a big money maker is Francesco Del Balso who has in past years been touted as a "Capo" as far as such structure may or may not currently exist.