A friend from work's dad died. I went even though I'd never met him.
Of course you did. That's what people do.
Someone you know lost their Dad, of course you went and paid your respects.
I can't count on all my digits on my hands and feet the number of times I've done that.
Of course, usually going to a colleague's family funeral doesn't involve 3 days leave away from the family at short notice.
If it did, I think you'd be looking more at a friend from work than just a mate from the office.
I've said in all my posts that if this dude is close to the family that what I'm saying doesn't apply.
But there is no indication of that here. His own partner thinks he's going for the fun times.
Funerals are not parties. You go to pay your respects to the bereaved.
If he doesn't know the family, and didn't know their daughter well when she was alive, then what is his business there?
If he was nearby and going was not a 3 day commitment, then I would say he should go.
But this is too much for someone he didn't know well when he isn't close to the family.
I'm usually the person encouraging people to attend funerals when they are unsure. But just because it's a funeral doesn't mean you should definitely go, no matter what.
And I'm speaking here in the capacity of person far more likely (by a significant margin) to attend a funeral in my marriage. I wouldn't bugger off for 3 days at zero notice to attend the funeral of somebody I only knew in passing. That's just a pisstake.