The importance of the cameo is unknown at this point, so if Clemons did decide to walk, Justice League director Zack Snyder would simply cut the scene out, find a way to work around it and/or recast the role of Iris West, as needs be.
Prior to leaving, Famuyiwa and the studios had brought on Kiersey Clemons to play the female lead in The Flash, Iris West.
For the time being, it appears as though Clemons is still part of the DCEU and will even debut as Iris West in next year’s Justice League.
After joining The Flash earlier this year, director Rick Famuyiwa has now left the project, citing creative differences with the studio(s) regarding the direction and tone of the film.