Absolutely - I didn't say anywhere that it was what she signed up for. Nor did I say taking 3 children to a festival was the only alternative to staying home. I was replying to someone who said she couldn't do it and I must be a better parent than her - I was making the point that when you're on your own, you just have to do things OR you'd be home all the time.
As I've said (now twice), I was replying to the person saying that it wasn't possible to do it with three children on your own. It is. Whether it's something they'd enjoy depends on the type of person they are, I get that it's subjective. But we aren't talking about babies here, the eldest will either be at the end of year 6 or 7. No reason it couldn't be fun still, even if it's not what OP had initially thought was the plan.
Again, as I initially said, her husband was wrong for not checking dates (who in a marriage books a trip abroad without running it past the other person) but the options now are make him cancel (he clearly doesn't want to so it would be forced even if its the right thing to do) or take the kids by yourself, have a bit of independence and realise you can manage things alone, or he goes on his holiday and OP stays home. No other options really.
Not a single bit of me would care about going alone with 3 kids of that age, nor would I want to spend the time with someone who clearly hadn't wanted to be there.
The OP was asking for opinions, that's mine. Might be different to yours, or hers, but it's equally valid.