Well, its far too fragile to survive. Poland and Lithuania union was quite weak at times, especially at the earlier period, when the interests of countries were not mutual; here its even worse. Lithuanian interests are not hungarian ones and the other way around - it would be mostly Poland helping one or the other since only it may share some interests (being in the middle).
Furthermore, Teutonic threat to Poland is far weaker, not forcing Poland into union. If the PoD is at time of Henry Probus, then Poland is propably united around 1300, and certainly with Silesia (at the time richest polish province) of which Probus was prince. Teutonic Kinghts will propably not be capable of taking Pomerania from thus strenghtened Poland, and after union with Hungary, they are far too weak to threaten the dual state. Union with Lithuania would be quite resource draining in the long run, and there no reason for it; though they may become allies (Lithuanian christianity comes from Poland, but without any stronger ties), with dual state using Lithuania as counter against teutonic knights.