No it isn't worth 'breaking up a family' (although if that happened, it would be him doing it, not you - the problem has come from him) for one night of thoughtless behaviour. It's already more than that though, isn't it?
He's come home and instead of being shamefaced at being in the state he is when faced with his baby at home, he's taken himself off up to bed and when you've asked him to take his turn at parenting, he's simply said No. Just 'No - he's going to sleep off the drugs.'
So it's not 'just one night'. 'Just one night would be a tired, red-eyed and shamefaced DH currently sitting with your DS taking his turn after apologising profusely and saying it won't happen again. That's what would be defintiely not worth splitting up over.
A bloke who thinks it's just fine to do what he has, and after that also just fine to inform you that after you've taken on his parenting load for 36+ hours straight, you can fuck off if you think he's giving you a break as he deserves to recuperate from his drug binge.
Now that has all the hallmarks of being not at all fine and very much something worth splitting up for.
So I suggest you have a tlak with him when the delicate flower has recovered and tell him calmly and factually that if he takes drugs again, you will leave him, because you have no intention of being told by your own husband that he can't take his turn at parenting because he's on a drug comedown. Oh and YES you would be quite happy to tell anyone who asked that that's why you left. :)