Guesses based on story so far
What is really happening in the last scene
1. Rachel really has turned and serves Mindlos, Game is over MC loses as Rachel knows where the MC was living, and where all the girls are, for her to have been co-opted means player has lost. No way to continue.
2. Rachel wasn't mindcontrolled by Mindlos, due to him noticeably lying to her enough that her mind fought the attempt, explains why she wasn't facing him when she said she'd do what her master commanded, and why she didn't kill the Mother.
3. Rachel was mindcontrolled, but regains control due to Mindlos forcing to much too quickly, similar to 2, only needs a little push to come back to the MC
All 3 are possibilities, but Id doubt the first, the second is the most probable
We know the character never lied to Rachel, he omitted facts until he could tell her them, but no outright lies, and eventually he did tell her, so yeah when Mindlos told her he had lied to her as a way to take her away from him, and when he said the MC didn't care about any of them she knew that was a lie, she told the MC herself that he seemed to care so much for them all, Rachel's subconscious would have rebelled.
No character that had been effected by the powers had ever been converted from one master to another in one go, and then only because of the Source power the MC and Victoria have, Mindlos's powers might be stronger or just faster, but I doubt they would be both (He went from your power, to his in one step, and considering he made that jump in a short time its doubtful his power increased that much, especially since he is suffering some of the side effects, worse than the MC is now), she would only have looked at the MC, when saying she'd obey her master if she still had control and he was still her master.
Mindlos's protector has been commanded not to act until he commands it, meaning Rachel can act against him, and as long as he doesn't get a command out Donna cant even draw a weapon.
Never is it said anywhere that the Source power only effected the original version of the Gift, in fact Mindlos wanted control of her due to her power, which the MC also has, which mindlos doesn't know, and the source power might have helped Rachel protect herself from Mindlos's control.
Also if Rachel was under Mindlos's control Rachel would have already killed one of the MC's friends, she never got commanded to stop, and she couldn't even say master when she got the order.
And right at the end, Rachel is in the perfect position to get rid of Mindlos once and for all, bite his dick off, grab the gun, shoot him, player commands all three to serve him, reinforce Rachel, start control of Donna and Miranda, because the MC knows it takes more than one attempt, also his source power would be affecting them all through this, Donna is already rebelling against Mindlos in her own ways, as is Miranda, so my guess is both would happily switch.
Someone mentioned Rachel actually sucked him off, at the end of the cliffhanger, she still hasn't done that so, unless they did something wrong, that hasn't happened she was only kneeling in front of him, in position to bite it off hopefully.
In addition to all this, there are three to four main reasons this is the way things would be going
1. I doubt the Dev is ending the game at this stage
2. MC has his phone chances are his "girls" are probably in position to raid the place
3. Dev has stated in the past there wouldn't be any rape, for Mindlos to have any sort of sex oral or otherwise with Rachel or the MC's friends its a direct counter to that.
4. Dev has already gone against one promise, that you'd get them back in 0.8, to break two would drive people away from the game especially if it was rape against those that the MC has lived to protect. Considering that was another of his statements, that full on NTR and Rape wouldnt show in the game.
Dev has said to some people the Kidnap arc will be over in the 0.9, If thats right, either we get them back or hes ending the game, so I'm hoping we get them back. No point in continuing if you don't have your closest "family"
Also I doubt the MC would hold back at this point, he would want Mindlos dead, so hopefully thats part of the 0.9 big events.