Do I need to include ‘else’ and/or ‘endif’?

You just need an else block:

//templating syntax
if($condOne):
    //do stuff if $condOne is true
elseif($condTwo):
    //do stuff if $condOne is false and $condTwo is true
else:
    //do stuff if both $condOne and $condTwo are false
endif;

//braces syntax
if($condOne){
    //do stuff if $condOne is true
}elseif($condTwo){
    //do stuff if $condOne is false and $condTwo is true
else{
    //do stuff if both $condOne and $condTwo are false
}

Regarding “it’s probably good practice to finish with ‘endif'”, endif is only used when you are using the templating syntax:

if():
    //do stuff
endif;

the alternative is regular braces syntax:

if(){
    //do stuff
}

The former is preferable when you are outputting html by dropping out of php with a closing php tag, because an endif is easier to match up than a closing brace:

<?php if($someCondition):?>

   <h1>Hello <?=$userName?>, how are you today?</h1>
   <ul>
   <?php foreach($someArray as $key => $value):?>
       <li><?=$key?> : <?=$value?></li>
   <?php endforeach;?>
   </ul>

<?php endif;?>

VS:

<?php if($someCondition){?>

   <h1>Hello <?=$userName?>, how are you today?</h1>
   <ul>
   <?php foreach($someArray as $key => $value){?>
       <li><?=$key?> : <?=$value?></li>
   <?php }?>
   </ul>

<?php }?>

However when writting code that does not drop out of php mode, the latter is far more common and arguable easier to read:

$out=[];
if($someCondition){

    $out[$username]=[];

    foreach($someArray as $key => $value){

        $out[$username][] = $key . ' : ' . $value;

    }

}