Your nerd rage would be tedious enough if you were an actual rules lawyer pointing at the actual fine print of a spell effect that is precisely defined in the official rules (god knows we have enough rule lawyers in these forums as it is)... but you've managed to achieve the astounding feat of being just as irritating as the most bombastic sort of rules lawyer preening over his technical correctness, WITHOUT the sole redeeming quality they usually have of at least being technically correct.
There is no fine print for you to HAVE a technically correct point about. All you have to work with is a vague assertion that the spell slots would be "replenished", whatever that means. And it deserves to be stressed that this vague description came from a TRIUMVIRATE OF INFERNAL BEINGS! When you're LITERALLY dealing with devils, don't be surprised if the devil is in the details.
Speaking of which, did anyone else notice that when the demons said that each of them would get custody of V's soul for a period of time, they never actually promised to wait until after he's dead to act on their option? V clearly assumes so, but they didn't say it. Won't V be surprised when he gets to the gate, and they call in their half of the bargain? That's what happens to people who think they can make "sensible" assumptions while bargaining with infernal beings.