I've been on that flight - similar situation.

While on board you should expect to be given a Customer Service Letter (inconvenienced pax). Based on Class of service, *A level - you should receive by mail, within weeks a CS voucher - this comes automatically, no begging.

Upon arrival at GRU (now late evening):
a) if staying in SP you'll be offered a free taxi ride to hotel/home
b) if continuing elsewhere, UA will accomodate you on the next available carrier, eventually overnighting at a GRU Hotel.