MON need B757s for some of the airports they operate to such as some of the Greek Islands and correct me if I am wrong but I don't think the A321 can reach Egypt, I may be mistaken.
The BA 757s are quite young and certainly have a huge life ahead of them in passenger service before DHL get their hands of them but obviously we have to see what happens with the trading.
Will be a great shame to see the end of an era for another 757 legacy carrier.