Without men like +Williamson it will.
Tradition will never slip into irrelevance.
True tradition won't. Thus, the SSPX will slip into irrelevance.
Bishop Williamson is the greatest reason why not to take the SSPX seriously. I have yet to meet someone form the SSPX to even make me think about what they teach and do. In fact, the only thing the SSPX has led me to think about is the validity of teachings of the Catholic Church, themselves included. While I was never a Traditionalist, the SSPX has played a good part in pushing me towards Orthodoxy.
The memory of God should be treasured in our hearts like the precious pearl mentioned in the Holy Gospel. Our life's goal should be to nurture and contemplate God always within, and never let it depart, for this steadfastness will drive demons away from us. - Paraphrased from St. Philotheus of Sinai
Writings from the Philokalia: On Prayer of the Heart,
Translated from the Russian by E. Kadloubovksy and G.E.H. Palmer, Faber and Faber, London, Boston, 1992 printing.