12 Villains Who Must Appear In Affleck's Batman Movie
4. Harley Quinn
If Harley steals Suicide Squad in the manner that's already being set up, there's surely no way Warner Bros won't then immediately set up a plan to take further advantage of brand Quinn. One possibility would be to give her and the Joker their own movie, with Batman as a supporting character, but making her next appearance a cameo in the Batman stand-alone would make marketing sense.
If the Joker is going to be the big bad of whatever story-line Affleck has chosen to adapt, it would make sense that he would reclaim his favourite play-thing as a side-kick. And no matter how nice it will be to see an empowered Harley operating as a lone wolf, narratively speaking, it makes far more sense to have her aligned with her "Mr J", with her lunacy manifesting as adoration for her "creator".
If she doesn't get killed off in Suicide Squad - come on, it's not likely - it's inevitable we're going to see her again.