существует ли лист

Function Sh_Exist(sName As String) As Boolean
    Dim wsSh As Worksheet
    On Error Resume Next
    Set wsSh = Sheets(sName)
    Sh_Exist = Not wsSh Is Nothing
End Function
 
Sub Add_New_Sheet()
    If Not Sh_Exist("Новый лист") Then
        Sheets.Add(, Sheets(Sheets.Count)).Name = "Новый лист"
    End If
End Sub