Does it have to replace credit money?
In my opinion; of course not. Although credit money and bitcoins are not necessarily antagonistic, as ripple demonstrates.
If what you have been saying is true, it should cause economic collapse without even having to compete with credit money as currency, its mere existence should be enough.
no, why?
Its deflationary nature is only a problem for bitcoin to become a mainstream currency, or it could be a problem for the economy if it somehow were forced on us. But the mere existence of something that can store wealth and cant scale with the economy is no threat to the economy. For argument sake; there is only a limited number of Rembrandt paintings; that may make it a worthwhile investment; but I dont see why that would wreck our economy. Then again no one claims we could use rembrandt paintings to replace credit money, and if we were to try it anyway, I think we can agree it wouldnt end well.
No, I'm just perfectly convinced that the deflationary aspect will not hinder its usage in commerce. The claimed harmful effects of deflation seem to focus on the investment aspect.
Its rather the opposite.