I will bet right now none of those characters are returning except maybe Bolo Santosi as an easter egg.
The above 8 characters save for two never appeared in Just Cause 4. Di Ravello "returned" as a cow in Just Cause 4 but he is dead. And a ghost haunting Rico is almost unheard in the Just Cause Universe.
Gabriela Morales may have defected to the Army of Chaos when she gave Rico Oscar's plane location (or at the very least left the Black Hand), but she was never seen again after Operation Illapa. Coupled with her only other appearance in Operation Whiteout, she is essentially a minor character in Just Cause 4 at best.
Mira might have suggested "having an army is a good idea" but she is never heard of again during any of the DLCs. To me, that means the character is done.
While Mario may have been a high ranking member of The Rebellion, he now operates Frigo and Etcetera. He can't just leave his business behind like that.
And Miguel... well... maybe he was never shown being killed in Just Cause 4, but the chances of him surviving Di Ravello torching his household are... almost zero. Rico was specifically stated to be orphaned as a result of Di Ravello's actions. Orphan means no parents. Hence, Miguel is probably dead.
Bolo Santosi is the only character that has appeared in every game except for Just Cause (1). Her appearances in Just Cause 3 and 4 were only cameo appearances as easter eggs, but it's highly doubtful she will return to Reapers leadership if she's a successful DJ now.