If the character survives this game, but retires after MK:A, what role could they play for the next-generation fighters? Well I see Scorpion returning somehow as he's still the Elder Gods' Enforcer (hopefully they'll do more with him than that but...) and either Sub-Zero or his successor.

But for me I wouldn't seeing these characters play some kind of roles in the next-generation...

Fujin: I imagine he'll take Raiden's place...

Liu Kang: Whether he lives or dies, I imagine that Liu Kang will be this legendary hero that the next-gen fighters all look up to and are awed by, there would be statues of Liu Kang in Earthrealm, Edenia and (depending on what happens there) Outworld. If he lives, he could be mentioned as ruling Edenia with Kitana with their son as a fighter, but the first part could work whether he lives or stays dead. I think Liu Kang will surpass even the original Kung Lao in terms of greatness and legends. (Well, couldn't think of a better way to put that but...)

Kung Lao: He could be something like the "Obi-Wan Kenobi" to the next-gen fighters, guiding them and teaching them the ways as I don't see him really actively fighting, before being struck down by Darth Vader that is...

Kitana: She could be mentioned as ruling Edenia as its new Queen.

Sonya and Johnny Cage: They could have a child, who fights in these next-generation battles.

Well that's all I've got for now...