It does happen in instances like the one in the O.P where the tenant just disappears and doesn't hand back the property .
Even when the tenant leaves and deserts the property, the landlord still needs to go to Court to legally get his property back, and that can take 6-12 months , otherwise its counted as an illegal eviction (without the Court order).
Also , the landlord may take a few months to find new tenants and he can sue the previous tenants for the void period