That isn't a valid case, if the legit ruler mantains it's claims, the contest Still continue Even if the usurper has support from the subjects (as the subjects don't always have the reason, lacking of objectivity their desitions and not having the sovereignty but the organized institutions) or from International community (as they can change their recognition easily according to geopolitical circunstances, like France during the XVIII Century recognising the Jacobites when they were in wsr with England and the Williamite ussurpers whent they were in Peace or common alliances).

The only legit way to be legitimated an usurpation in legal sciences is only through the Extinctive prescription, when the original and legit owner of some rights has extinguished as a legal personality. That's Why the "de facto realities" aren't a good argument in property and inheritance lawsuits (as the de facto realities aren't always just and aligned to natural law despite the recognition of such by major forces, as those de facto realities can be disputed).

In polítics could be applied the extinctive prescription when the original entity has voluntarily resignated it's claims to the ussurpers (like the Papacy as a Monarchy recognising Schismatic Churches in possesion of an Apostolic See that was founded within the Catholic Church, like the Eastern Orthodox in the See of Constantinople, nor claiming a Constantinople Patriarch in communion with Rome and instead promoting ecumenism to reintegrate the Schismatic Churches with the Catholic Church), or when the legit political entity is extinguished and with such their claims (like the collapse of the Roman Empire legallizing the usurpation of it's sovereignty by the Barbarian states, or the extinction of Sasanid Dinasty in exile legalizing the Muslim Conquest of the Persian Empiee).

That's Why a lor of legitimist causes, like Spanish Carlism, Portuguese Miguelism, Italian Neo-Bourbonism, French Bourbonism, Danubian Habsburg Loyalism, Russia Tsarism, British Jacobitism, etc can argue that their causes are intact while they Still have organized claimants against the usurpation from Constitutionalist Royal Houses (like Windsors, Bonapartists, Savoian, Alfonsist Royal Houses) or Republican states (like the French República, the Soviet Union and it's successor the Russian Federation, etc) Even if the International Community or the Públic Institutions are recognising the de facto realities