Loop through your query to send all the emails. See the change in bold where you get the address from the query as move through each record. Syntax might not all be right in that code but that's the idea.
Dim db as database, rs1 as Recordset
Set db = Currentdb
Set rs1 = db.OpenRecordset("qry_EmployeeTerminationNotice")
rs1.movefirst
Do Until rs1.eof
vTermText = DLookup("[YourTextField]", "qry_EmployeeTerminationNotice")
DoCmd.SendObject acSendQuery, "qry_EmployeeTerminationNotice", acFormatXLS, rs1!EmailAddress", "", "", "Termination Notice", vTermText, True, ""
rs1.moveNext
Loop