Delete worksheet if it exists and create a new one

Instead of looping through Worksheets, you can test the existence of an item in the collection by trying to get it:

Function GetWorksheet(shtName As String) As Worksheet
    On Error Resume Next
    Set GetWorksheet = Worksheets(shtName)
End Function

If Not GetWorksheet("asdf") Is Nothing Then
    Application.DisplayAlerts = False
    Worksheets("asdf").Delete
    Application.DisplayAlerts = True
End If
Worksheets.Add(After:=sheets(sheets.Count)).name = "asdf"

However, the most straightforward method would be trying to delete the sheet while wrapped in a On Error Resume Next - On Error GoTo 0 "block":

Application.DisplayAlerts = False
On Error Resume Next
Worksheets("asdf").Delete
On Error GoTo 0
Application.DisplayAlerts = True
Worksheets.Add(After:=sheets(sheets.Count)).name = "asdf"

Remove the End statement, your code terminates after finding and deleting the worksheet asdf.

For Each ws In Worksheets
    If ws.Name = "asdf" Then
        Application.DisplayAlerts = False
        Sheets("asdf").Delete
        Application.DisplayAlerts = True
    End If
Next

Sheets.Add(After:=Sheets(Sheets.count)).Name = "asdf"