American colonial boundaries were established as the result of interactions between the government and courtiers in London, which is a reason not to accept reactionary arguments about states’ rights today. The new American government created a clear process to convert property outside the existing state boundaries into new states. Would the British government have done the same, if the Revolution had failed?
No. The British government would have continued to try and enforce the Proclamation of 1763, which did not envision a need for any new political entities. Those efforts would have failed, so at some point, given the condition of American communications and transportation facilities, it would have become obvious even in London that property west of the Appalachians needed its own governments. The boundaries of the new colonies, however, would probably have been thrashed out in the same manner as before–on an ad hoc basis, with the interests of powerful courtiers predominating. As a result, the map of British America would have looked a lot different than it does today.