This seems like a slightly about face way of doing this.

I'd suggest you'd be better to make the subject come from the controller rather than trying to scrape it from an apex param on the URL.  In my experience the server side redirects associated with page refreshes tend to lose the URL parameters.

Try the following:

<apex:page standardController="Applicant__c" extensions="view">

<script type="text/javascript">
      function getSelectedID(id) {      
          
          viewFunction(document.getElementById(id).value);
          
      }
      </script> 
  <apex:form >
  
  <apex:actionFunction name="viewFunction" id="vfunc" action="{!getApplicantByStatus}" rerender="view">
      <apex:param name="para" value=""/>   
  
    </apex:actionFunction>
  
      <apex:pageBlock title="Hello {!$User.FirstName}!">
          <apex:outputLabel value="Status :" for="status"/>
          <apex:inputField id="status" value="{!Applicant__c.Status__c}" onchange="getSelectedID('{!$Component.status}');">
                            
          </apex:inputField>
      </apex:pageBlock>
      
       <apex:pageBlock >
           <apex:panelgroup id="view">
              <apex:pageBlockTable id="viewApplicant" value="{!applicantNameByStatus}" var="app">
              
                  <apex:column headerValue="Applicant ID">
                  <apex:commandLink reRender="detail" value="{!app}">                  
                  <apex:param id="cid" value="{!app.id}" assignTo="{!chosenAppId}"/>
                         </apex:commandLink>                        
                  </apex:column>
                 
                 
              </apex:pageBlockTable>
           </apex:panelgroup>
      </apex:pageBlock> 
      
  
 
</apex:form>
<apex:outputPanel id="detail">
<apex:actionStatus startText="Requesting...">
<apex:facet name="stop">

<apex:detail subject="{!chosenAppId}" relatedList="false"  title="false"/>
</apex:facet>
</apex:actionStatus>
</apex:outputPanel>

</apex:page>

Controller:

public class view {

    public Id chosenAppId {get; set;}

    public view(ApexPages.StandardController controller) {

    }


    public Applicant__c applicant;
    public List<Applicant__c> applicantByStatusList {get;set;}
    private ApexPages.StandardSetController controller;
   
    public List<String> applicantNameByStatus{
        get;
        set;
        
        }
    
    
    
    
     
    public view(ApexPages.StandardSetController controller) {
        this.applicant=(Applicant__c)controller.getRecord();
        //this.controller = controller;
    }
    

    
     public PageReference getApplicantByStatus(){
     
    String para1=Apexpages.currentPage().getParameters().get('para');
        
         applicantByStatusList =new List<Applicant__c>();
         applicantNameByStatus=new List<String>();
         System.Debug('PARAMETER :: '+para1);
         applicantByStatusList =[SELECT Name,Name__c,Status__c,Interview_Date_Time__c FROM Applicant__c WHERE Status__c =:para1];
         
        
         for(Applicant__c a:applicantByStatusList){
            String name=(String)a.Name;
            
              applicantNameByStatus.add(name);
               
            }
          
         
         return null;
    }
}