[1and1]

Easier to do it yourself and have control for future edits if needed- It's just using Data Validation.

To allow the list of names to be extended you just have to tell it the source list is longer.
1- select the name drop down cell (2C)
2- on the Data tab click on Data Validation
3- Change the Source line, increasing the last number reference
3a- Original: ='List of Employees'!$B$4:$B$8
3b- New: ='List of Employees'!$B$4:$B$108

This adds 100 more lines to the data source list- extending it down to B108, instead of just B8. As you add names to the list they will be added to the drop down. You will not just get blank entries in the drop down- it's smart enough to just show populated values.

The same change will update the Employee Leave Tracker tab automatically so you won't need to make additional edits on that tab.

Where it uses Named Ranges, for example Leave Types, the named range will expand dynamically as you add additional leave types.