How I think the beginning will play out
My idea of how Dom and his son will escape the dam after the Fast X ending
Mr Nobody and Little Nobody arrive in a helicopter (Little Nobody should be fine by now, he just rolled out of his car in Rome), one of them hack the bombs at the very last second and take Dom and Little B to safety and plan something againts Dante. I guess the crew (Roman, Tej, Han and Ramsey) in the plane will save themselves with Deckard's cars.
If Tess is still recovering in hospital from the sniper shot, she cant really help. Maybe she contacts her dad, Mr Nobody gets upset that her daughter got hurt and gets motivated to return to help Dom and the crew. Eventually he learns from Dom that Aimes went rogue and is working for Dante