As one who holds true to Papal Loyalty and Papal infallibility, if it should happen in my lifetime, that one day the Magisterium of our Roman Catholic Church could fall so clearly far from the true and sound doctrines, dogmas, and traditions of our faith, that they deliberately take steps to misguide the Faithful, thereby leaving the faithful to wonder how they should act toward them, without breaking away from them, while still remaining true to the Holy Spirit and Holy See that guides our Church... Has it ever happened in the history of our Church?

The Magisterium of the Church has never, so far, deflected from the Orthodox Teaching of Christ.

Can a priest consider himself faithful to the Holy Father and the Magisterium and at the same time celebrate Holy Mass for particular groups such as Dignity, SSPX, Society of Pope Pius V, Catholics for Free Choice or Call to Action?

To be faithful to the doctrine of the Church, you cannot say mass for Dignity, Catholics for Free Choice, or Call to Action. Cardinal Ratzinger and other Roman authorities have made it quite clear; SSPX and SSPV Masses are perfectly acceptable.

What words are needed at consecration to validate a Novus Ordo Mass? When a priest speaks the words of Consecration out loud in an invalid manner, should we presume that the priest is whispering the right words under his breath thereby making it a valid sacrament?

The words of consecration, said out loud or whispered, are "This is My Body" and "This is the Chalice of My Blood: which shall be shed for you and for many unto the remission of sins".

You cannot presume that every priest who whispers the words of consecration whispers the right words if you cannot hear what words are said.

Did Archbishop Lefebvre reconcile himself to the authority of the Holy Father?

Archbishop Lefebvre never renounced his allegiance to the Papacy and to the Holy Father.