I didn't feed to sleep, but was required for all nights and wake ups for the first 12 months.
Firstly, for a one-off special night (say you needed to attend a wedding or something like that), baby would manage it would be very different to a normal night. Maybe whoever looks after baby ends up sitting watching tv while holding baby at 2am. Or goes for a 4am drive with baby in the carseat. But baby would soon catch up the following days, so it is doable even though baby wouldn't have a 'normal' night.
On a more regular basis, I guess priorities just change. My 'baby' (nearly 3 now) is our fourth so we have over a decade of parenting behind us. DH and I value sleep and responsibility-free time far more than a night out or alcohol. So we have our couple time through child-free lunchs and breakfasts when someone else takes the children. Or indeed just staying at home while children are with grandparents for the morning.
If you do want a night out, not leaving until hold is in bed makes like easier. Then being prepared to either let baby get up and have a different routine, or come home yourself, if baby can't be settled.
As for baby who is attachment parented settling a different way routinely for someone else, tgi s probably won't be to do with milk. It's the act of breastfeeding baby finds comforting, not the milk. So bottle/cup use is largely irrelevant to sleep, therefore no specific need to push for milk from anything other than the breast.
Comfort when you are not there would probably come in the form of a comforting action (one of my dc used to rub his fingers together, another liked to rub the hair at the back of his neck, for example) or special toy/blanket/object that baby may (or may not) bond with.
The very earliest that's likely to begin to establish is around 12 months, with fine motor skill developments. But it may not at all, so realistic expectations will be necessary.
What will probably come first for the attachment parent is baby sleeping through, before baby settles easily independantly. This therefore allows for nights out even though baby is not an independant sleeper, just you don't go out until after putting baby to bed, not before.