#4 Not the right time for Brock Lesnar to return
The most probable scenario that could happen now that Brock Lesnar is a free agent is that he will not sign a contract anywhere else. That's how it has been over the years, and we expect nothing to change.
We know that Vince McMahon will never allow anyone else to sign Brock Lesnar, if he still has plans for The Beast Incarnate. This is why Lesnar didn't fight Daniel Cormier in UFC. McMahon offered a much better contract to The Beast than Dana White could.
A WWE Hall of Famer isn't a John Cena fan. More details HERE
2020 has been a turbulent year for WWE, and although they didn't cease their operations when the world was in lockdown, they had to have their shows without the presence of the fans. Lesnar is a household name and it doesn't make sense to bring him back at this moment. WWE, probably, isn't ready for Lesnar's return and there are currently no plans for him from a creative standpoint.
Maybe next year, when fans will be allowed to attend shows, WWE could bring Lesnar back for WrestleMania 37. The current rumors for him are to face Drew McIntyre at the Shows of Shows next year.