The beauty of component framework is events .You can make two components talk to each other via events .All you need to do is handle the event when the case record is created in another component and use Navigation to redirect to needed page
Here is sample component you need to create for that
Create a component like below
<aura:component implements="forceCommunity:availableForAllPageTypes">
<aura:handler event="force:navigateToSObject" action="{!c.navigate}"/>
</aura:component>
The handler controller logic for same is as below
({
navigate: function(component, event, helper) {
var sobjectId = event.getParam("recordId");
console.log(sobjectId);
if (sobjectId.indexOf("500") >-1) { //Note 500 is prefix for Case Record
var urlEvent = $A.get("e.force:navigateToURL");
urlEvent.setParams({
"url": '/case/'+sobjectId,
"isredirect" :false
});
urlEvent.fire();
}
}
})
Drag this component on the case creation screen using community builder .