Fucking nasty selfish wanker !
He's a hypocrite - You'reBeing is absolutely right, why the hell is 6.30 too late for her, but 7 okay for him ?
And he's a liar ...... "too sick" to look after his own children, but not "too sick" to neck a load of booze which would make anyone genuinely nauseous feel even worse.
Your friend needs to TELL him she's going out, and just go, right there and then, before he convinces her to talk herself out of it for some spurious reason which then enables him to have an easier life in one way or another. I'd never normally advocate such a course of behaviour BTW but this is an example where fighting fire with fire is more than justified.
I wonder how much of his "work related" wining and dining is genuine ? So very easy for someone in his position to lay on the guilt re: "working long hours" thereby giving themselves unfair me-time where he forgets he's a parent and a partner, and can do what the fuck he likes. But hey, that's okay isn't it, because it's work don't you know and little wifey would be bloody ungrateful if she had the temerity to ever question this. Does she even know for sure that he's schmoozing with work contacts at all, or is this a cover story for more boozy nights out with friends ? Even if it were customers, colleagues, networking and so on, does the amount of time he's out (and unavailable for dad duty let alone working on his relationship) actually reap reward in proportion to what he's otherwise avoiding I wonder ? i.e. how much new business does he get as a result of all this ? .....
.... obviously, am just hypothesising here and have no idea of the real situation. But your friend should certainly be fully involved in what his movements are. I get the feeling from the little you've told us that she's kept in the dark about what's going on. The thing about "chances are he's got a work thing that evening" ..... yet he doesn't discuss this with her in advance (she only finds out at the 11th hour when he comes home - only to go out again), just assumes that she'll be there, in her rightful place, looking after the kids which are just as much his as hers. I can accept there may be occasional last minute work demands in many jobs, but am finding it hard to swallow that this would happen on such a regular basis. Seems like he doesn't feel he should have to tell her anything he doesn't want to. Arrogant pig - obviously he is by far the most important person in the house isn't he ? (in his eyes).
(disclaimer: apologies for going off on a bit of a rant. And maybe projecting. Past bad memories and all that ...)
But in a nutshell, she needs to start asserting herself and insist upon a way forward where they both get free time. If he can't, or more likely won't pull his weight then at the very least he should enable her to have some semblance of a break by paying for sitters, cleaners etc.
And having such a selfish and dishonest partner who couldn't give a stuff about my wellbeing and need for a relatively tiny break (compared to his) on very odd occasions would be cause enough for serious thought about LTB - IMO.