Possible contenders:
Frol Kozlov: He was considered Khrushchev's number two until the mid-1960s (he died in 1965). In 1959 Time Magazine even put him on the cover an asked if he was Khrushchev's successor. Kozlov was considered to be a leading force in the conservative anti-Khrushchev group. The big problem is that Kozlov was not very intelligent, being described by Alexander Shelepin as "a very limited man." Of course the same was often said about Brezhnev, but on the other hand the stereotype of Brezhnev as an intellectual weakling comes from his latter years (when multiple strokes and other health problems severely incapacitated him).
Leonid Brezhnev: The most boring choice, because it would basically be the same as OTL. Brezhnev wasn't as senior at this stage as he was in 1964, but he was a senior member of the Khrushchev team, and as OTL shows he had the low cunning needed to succeed in power struggles.
Alexei Kirichenko: Another candidate for Khrushchev's number two, being the second-most powerful person in the party. His biggest issue is that he wasn't Russian. and while that didn't stop Stalin the CPSU was much more accommodating of non-Russians being the top leader in Stalin's day than in Khrushchev's.
Alexander Shelepin: At the time Shelepin was head of the KGB, so he would first have to move from that position to something else, meaning that there would be someone in the interim. Shelepin was considered one of the biggest Stalinists in the government, and was known as a Machiavellian schemer. However his colleagues knew this, and they were all very nervous of him after Khrushchev's fall IOTL. ITTL might go similarly to IOTL, with Shelepin having a leading role at first but quickly being sidelined by his rivals.
Mikhail Suslov: one of the chief ideologists of the Soviet Union and an extreme hardliner. The problem is that Suslov never wanted supreme power, preferring to play the role of the grey eminence.
Anastas Mikoyan: By this point Mikoyan was one of the last of Stalin's cadres at the national level. He was a strong supporter of destalinization (he helped with the Secret Speech), and thus was one of the few reformers who could succeed Khrushchev. He also had a lot of experience on the global stage, which strengthens his profile. However he also wasn't Russian, and his support for reforms would make him an enemy of the reformers. He's also one of the oldest of the group, being a good decade older than most of the rest of the leadership. That's both a strength and a weakness. It's also unclear if Mikoyan ever wanted supreme power, since he really didn't make an attempt to seek it IOTL.
How it might play out: With the exception of Kozlov these people can rule into the 1970s or beyond. Kozlov was an alcoholic, something power wouldn't help, and had several health problems in the early 1960s IOTL. One interesting possibility is Kozlov winning out, then dying in 1964-1965 and being replaced by Shelepin.
Molotov just might get un canned. Leonid is not high up enough yet
Molotov and the rest of the Anti-Party Group aren't making a comeback. There were plenty of people who could have succeeded Khrushchev, and who actually had power and influence. By 1959 Molotov was nothing more than a figure from the past.