Scenario 1: if Yuno from world 1 (Yuno 1) killed Yuno from world 2 (Yuno 2) to take her place, wouldn't that take her out of the game? With that, Yuki could win and Yuno 1 would still be alive in world 2 that is, though she might have had to wait for the game to start before doing this.
Scenario 2: if Yuno came to world 2 in the past, she could break Yuki's phone before the game preventing him from entering, in which case she could win with Yuki still being alive.
Scenario 3: if Yuno 1 kept Yuno 2 alive and just hid for awhile, she could let them play out the game for awhile. When it gets close to the end, Yuno 1 takes out Yuno 2 and Yuki wins in another way. Yuno 1 could still be alive, though that would make Yuki mad considering it wouldn't have been his Yuno 2.
Could Yuno do these things to win with both Yuki and her being alive?