Among the leading contenders to take Rossi's place at Ducati are Yamaha Tech 3 riders Andrea Dovizioso
or Cal Crutchlow, who have both had their Factory M1 hopes thwarted by Rossi's return.
While his Ducati title dream is over, Rossi - who has taken 105 wins across all grand prix classes - still has a major record to aim for in the form of Giacomo Agostini's all-time total of 122 grand prix wins.
One more title for Rossi would also equal Agostini's premier-class crowns.
But after so long without a win - Rossi's previous longest GP losing streak was ten races, during his rookie 1996 season in 125cc - Rossi's first goal will simply be a return to the top step.
One major obstacle between Rossi and a return to victory, Casey Stoner, will also be removed from the equation next season.
Reigning double champion Stoner, the most successful rider since 2006 and Ducati's only MotoGP champion, is to retire at the end of 2012. Stoner moved from Ducati to Honda for the start of last season.
It is assumed that Rossi will again bring his loyal mechanics, led by crew chief Jerry Burgess, back with him to Yamaha.
In addition to Rossi, Lorenzo and Hayden, Dani Pedrosa
(Repsol Honda), Marc Marquez (Repsol Honda), Stefan Bradl (LCR Honda) and Bradley Smith (Tech 3 Yamaha) have also signed deals for 2013 manufacturer (non CRT) MotoGP rides.