You can access all of the keys:
gridView.DataKeys[rowNum][dataKeyName]
where rowNum is e.RowIndex from the gridView_RowDeleting event handler, and dataKeyName is the key you want to get:
<asp:GridView ID="gridView" runat="server" DataKeyNames="userid, id1, id2, id3" OnRowDeleting="gridView_RowDeleting">
protected void gridView_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
gridView.DataKeys[e.RowIndex]["userid"]...
gridView.DataKeys[e.RowIndex]["id1"]...
gridView.DataKeys[e.RowIndex]["id2"]...
gridView.DataKeys[e.RowIndex]["id3"]...
}