Cancel OR Loop Input On Worksheet Name

I am trying create a macro which asks for the Sheet name as an input for a Sub. I've gotten it to work but there is just one problem: The Cancel button does not work on the MsgBox. Everything else works just as I want to: it shows a dialog box to enter a name for the worksheet and if the worksheet does not exist, it loops and shows a message saying that it does not exist.

However, the cancel button does the same thing as entering nothing in the box and it does not end the process. I would want it so that the cancel button kills the process. Here is the code:

Code:
Option Explicit
Function WorksheetExists(WSName As String) As Boolean
On Error Resume Next
WorksheetExists = Worksheets(WSName).Name = WSName
On Error GoTo 0

[Code] .......