I am not sure why you would want to have a Donate Now button on a website for an inactive nonprofit.  There are now a couple of states among the 39 states and the District of Columbia with charitable solicitation registration statutes that don’t follow the old Charleston Principles and don’t give you a pass on registration if you are not actively soliciting within their state.  The new thinking of some of them is that you need to register merely because you have an operating button on the site that is accessible by residents of their state.  Although the likelihood of your getting into serious trouble because of an inactive site is relatively low, it is clearly safer to remove the button until you want to reactivate the organization.  You can always restore it later when you reactivate and you can decide at that time where you need to register.  In the meantime, you don't run the risk being found in violation of any state law. 

You could put a "Sign Up for Information" box on your website now if you think it might be worthwhile to collect contact info for potential future donors.  Asking for contact info would not constitute solicitation of a contribution.