Likely would just be renegotiated, however that can backfire on Virgin if Boeing push all initial slots to key customers like United, Ryanair, Qatar. Ryanair are another really putting the pressure on Boeing at the moment in regard to lack of deliveries.
QR cracked it over the delays to the -8 which meant others had to wait longer as they got earlier slots. All the reworks they had to do on the tail, well QR got all those slots in the first few months alongside Ryanair.
MAX10 is pretty critical to Virgin and its future success, Jetstar will have about 25 A321s before the first Virgin -10 even arrives.