Well, if NiGHTS becomes popular, and Sonic keeps getting worse, than a few things might happen. Here is a worst-case scenario:
Sega, fed up with the continually worsening performance of Sonic games, sells the IP to Nintendo, who promptly restores the franchise to greatness. Sega kicks itself in the head.
Sega takes NiGHTS and sets him up as the new company mascot, creating a massive franchise in the process.
After two or three very good sequels, Iizuka leaves the company. A new leader is found, and he takes the series into full 3D flight, in the game NiGHTS Adventure.
After NiGHTS Adventure is given the benefit of the doubt in reviews, who see this as a breakthrough and ignore the technical problems, Adventure 2 is released, which is also a hit.
After the Adventure duo are released, Sega falls to pieces because of financial problems, and puts out a string of bad NiGHTS games, trying to stay afloat.
Trying to give NiGHTS a darker side, a new game is released called Reala Into Dreams, which features the anti-NiGHTS as an gun-wielding, obscenity flinging motorcycle maren.
At last, all the entire franchise falls apart with the release of the abominable 2013 game entitled: NiGHTS Into Dreams. After being totally trashed by critics, Sega decides to sell the franchise to Nintendo, who immediately restore the games to greatness. Sega kicks itself in the head.
Sega takes Shenmue...