They won't go to SSPX. IME, most of those who attend indult, when it is taken away, go to novus ordo, or give up. That's part of the Masonic plan to condemn as many souls as possible.
I know quite a few families who attend Mass at the Franciscan Friary. Currently those friars still have permission to say the Tridentine Mass. My friends have said when that comes to an end, they will remain where they are and attend the Novus Ordo. They say they will "obey" even if it means they no longer have the Mass they "love."
I recently spoke to a woman I met at random in my area. She had a bumper sticker that said "I <3 the Latin Mass." She was wearing a scapular ( I could see the cord around her neck), so I approached her. I mentioned that if she was looking for a Latin Mass, I knew of several places but she would have to drive. She said the priest told her not to go to those "places." I left her my number in case she changed her mind.
IME, these people have sentimental attachments to some fantasy world--the 1950s, the old Mass, grandma's Bible. But they don't understand their faith, let alone love it. Very sad, but we must pray and never stop trying to help our Catholic friends find the True Mass and the Sacraments.