It would not happen as big companies in the top 100 where using/joining to use it now like Microsoft because they saw potential on it to be a good digital currency. Unless majority of it will pursue to make it illegal then it will be ban as they can influence the government to do something to it.
Dont say it wont happen. One thing I have learned is that anything is possible. And those multi-national you are saying, they exist within the armbit of the law. If countries decide to ban Bitcoin, what they need is to sign a Charter at the level of United Nations and thats it...
Now if it is banned, then its use will only be in a more secretive way but I am sure its total ban might spell doom because alot of people will abandon which will make the price come crashing...