It's not about dropping the charge. The CAS might uphold the ban, likely will in fact, that's irrelevant at the moment. When an appeal is filed against a decision it's often accompanied with a motion to stay the execution of the decision till the final determination of the appeal. The motion is often granted and the ban suspended till the appeal body's final decision is reached. It exists to preserve the right. Why you ask? So that on the off chance the arbitration body or court overturns the decision, the punished party isn't halfway into suffering an overturned punishment
TL;Dr the ban isn't alive if the appeal is alive
T
here's a surprisingly good explanation from goal in this article. If the CAS can hear and uphold Uefa's decision between now and CL registration we're in the CL