Thats pretty much what the wxample picture i posted does. The issue with your situation is you need a way to tell the projectile what is target is and if it missed the target. In the example i posted i solved the issue of knowing the target by having the target be any character hence the cast node, the knowing it missed is another matter which has so simple solution so i went with the idea if it hasnt hit its target after x seconds then it probably missed this is done witth the delay. Mow these methods ised are just an example and you need to come up wih how you want to define the conditions based on the context of your project.
You pretty much have made hhe first part of my example though you havent shown how you set the character reference and you used a more direct method decreasing health ( i would make use of the apply damage and event any damage nodes for organizations sake). For setting the character reference my method was to use a variable exposed on spawn so it could be set from the spwn actor node.
I posted this from my phone so excuse the spelling