The ASA have no powers. Rooney / Nike can carry on doing as they please. Only if ASA refer the case to a higher authority would the tweets be banned.
The ASA only offer guidance and assistance. They have the least teeth of all the toothless watchdogs we have in this country.
The only "crime" rooney / nike have committed is not indicating that the tweets were an advertisment.
It's happened before with celebrities promoting chocolate bars, toiletries and cars. I'm more amazed they would treat their fans with contempt just for a free lease of a Range Rover or a crate of Snickers.