You keep asking this question as if it were going to happen.
The SSPX's demands are the same demands it has made for years. The Vatican will not accept those demands, especially that one which the SSPX would like to use to supplant the Novus Ordo by allowing priests to, willy-nilly, use the Tridentine Mass whenever they want.
Fellay and company had best accept what JPII is offering; they're not going to get a more conservative Pope on this issue. There are those in the Vatican who would walk away from the SSPX and leave it in its schism.
The SSPX is not going to bend. An idiot like Williamson, with his fascination with the Unabomber, will heel to no one, least of all the Pope.