We study a model of dynamic monopoly with differentiated goods that buyers can freely dispose of. The model extends the framework of Coasian bargaining to situations in which the quantity or quality of the good is endogenously determined. Our main result is that when players are patient, the seller can sustain in equilibrium any payoff between the lowest possible buyer valuation and (approximately) the highest payoff achievable with commitment power, thus establishing a folk theorem. We apply our model to data markets, where data brokers sell marketing lists to producers. Methodologically, we leverage the connection between sequential bargaining and static mechanism design.