The fact that Offred, whether she survived or not, was able to leave a record of her time in the Republic of Gilead. Even if know-it-all professors are skeptical of her accounts, she was able to reclaim something that Gilead took from women: a voice.
The Epilogue reveals a few things: that the Gilead regime had ended and a new world was brought up, one where women regained their rights e.g. Professor Maryann Crescent Moon.
Similarly, the names of the professors and their respective universities also imply that Native Americans/indigenous Canadians have regained power, and developing nations like India have survived. In short, non-white groups have survived and the white-supremacist Gilead regime has not.
In the movie: Kate/Offred ends up killing the Commander with Mayday later rescuing her. She was true to her word that no one would take her baby or control her, and the shots of the battle between Gilead and the Rebels is nothing short of amazing.
In the book and especially the TV series, Ofglen is extremely brave. No matter what happens, she's determined to go down swinging.
For the TV series
Offred spitting out the bite of the cookie Serena condescendingly gave her.
This exchange from the TV series, which leads to Offred being clubbed in the head and electrocuted.
Aunt Lydia: Remember your scripture; blessed are the meek.
Offred: "And blessed are those who suffer for the cause of righteousness for theirs is the kingdom of Heaven." I remember.