[patent]

How long can the SSPX wait for it?

An eternity, it would appear.

At what point does the SSPX give up and decide to establish a more permanent parallel structure?

Well, they currently have their own seminaries, their own Bishops, their own convents, their own schools. It seems to me they already have established a permanent parallel structure, and do not plan on ever coming back. I don't know what else they need to establish to stay away forever.

patent  +AMDG

[ventana]

they would need to lay claim to the Chair of Peter.

[ultima ratio]

They have usurped no jurisdictions, but merely operate as any religious order would within the Church according to the mandate which had been provided by the Vatican itself. To suggest this is a parallel church is bizarre. They issue no new doctrines, have no new liturgical practices. Everything they think and do, in fact, is precisely as the Church had always thought and practiced. This, of course, is what bugs Rome. It wants the old Church and its version of Catholicism stamped out. That is to say, it seeks to erase the Church's memory of itself.

[Loyalist]

It seems to me they already have established a permanent parallel structure, and do not plan on ever coming back. I don't know what else they need to establish to stay away forever.

I think they would need to establish a formal curial and diocesan structure, complete with congregations and tribunals, before we could conclude that. Right now, all they have is the usual setup of a religious order.