Maumalo is averaging more than 150 running metres per game, and has become the crucial element at the beginning of their attacking sets. He has also topped 160 metres on six occasions, and was key to the recent wins over the Titans and Bulldogs.
And - like Vatuvei did as his career progressed - Maumalo is also becoming more than just a battering ram. Although he has a long way to go to match the extraordinary numbers of Vatuvei, he is developing into a genuine finisher on the flank.
Maumalo didn't score a try in his first seven NRL games in 2015, before grabbing a consolation touchdown in the 50-16 loss to the Cowboys. Last year, his return was similarly modest, with just one try from 10 games.
But in 2017 he has crossed for six tries, including the stunning 70 metre effort against the Bulldogs and other vital ones against the Broncos, Eels and Titans.
And defensively he has become more proficient. There are still things to work on, including a tendency for the arm grab, but Maumalo is becoming more proactive in defence.
His extension will soften the blow of Vatuvei's departure, which is expected to be confirmed by next week. Salford aren't the only suitors for his signature - there are other Super League clubs in the mix - but the Manchester team remain the most likely destination.
The final negotiations will be around financial matters. It hinges on whether Vatuvei will request a straight release from his contract in 2018, or some kind of compromise is reached where the Warriors may still pick up some of his salary next year.
There is also a chance that Vatuvei could request an immediate release, and play some of the current Super League season. This seems less likely though.