Can there be pointless duas? Mufti menk was asked what is the need for us to make dua for something we know is not going to happen. Like for example if a person is terminally ill is there a point in praying for a cure? 

There is a very great point! Allah (swt) is the Creator. He has created us to worship him. When you call out to Allah (swt) He is listening. Whether He gives you what you have asked is in His hands. 

Even when you see peoples condition getting worse, we have to keep home in Allah. Allah loves it when you call out to him with conviction.