"My son is 13 mo and we've finally, after much time and effort--but not including CIO--gotten him into a decent sleeping pattern; he goes to bed between 7 and 7:30 p.m. and usually sleeps through until 4ish, when he nurses for 15-20 min and then goes back to sleep until about 7 a.m. At the end of July, I'll be going away for 3 nights. So that's roughly my deadline for weaning him; this is the only nursing session we still do and I'm ready to be done.
I'm wondering if it's better to try to eliminate that feeding by having my husband go in when my baby wakes, for as many nights as it takes until he's sleeping through it; or if we should try to gradually push that feeding from 4ish to 6ish or later. Any thoughts?"
Before we go any further, I'm going to say that I think whatever nightweaning you do is going to go more smoothly as he gets closer to 14-15 months. They seem to be kind of clingy and in a little bit of flux around a year but get more independent at 15 months, so keep that in mind when you figure out your timetable for weaning. Also, teething could really screw you up, so all bets are off if he's teething and you might as well back off and just bide your time for a week or so while the teething is in full swing.
The first thing I think you should decide is whether you want this to be your problem or not. If you want to assume responsibility for it, then try pushing the feeding back slowly. It could work or it could cause a big early-morning struggle. I think it's honestly a crapshoot about how smoothly it will go.
If you want this to be your husband's project (which is the way I'd go, personally, because I feel like if the nursing is my deal then I shouldn't have to be point person for weaning, too) then you can either work on it now, or just let it happen while you're gone.
There are arguments for both ways. The argument for doing it now is that you'd be able to step in if it wasn't going well. You'd also know he was OK with going all night by the time you left. And the weaning would happen sooner than later.
The arguments for waiting until you're away are that he'd be a few months older so it would probably be easier. Since you won't physically be home, you wouldn't be tempted to give in and nurse (thereby prolonging things) and stomp all over whatever rhythm your husband and son have going together. Also, it would just be natural that when you're not there he doesn't nurse, so in some ways it would be less abrupt.
So I guess you have to figure out how involved you want to be in the process and let that be what guides you. Your son is going to be fine and will release that feeding eventually no matter which course of action you take, so it seems to me that this is more of an issue of division of nighttime parenting duties. I know how it splits up in my household, but that's not going to help you except maybe as a data point. But I do think it's totally valid to say to your husband, "You're going to be the only one in charge while I'm gone, so it's your issue to solve." You're not going to plan out all the other meals for everyone in the family for while you're gone, so this is just an extension of letting your husband really be in charge completely while you're away.
And who knows if your son will even wake up while you're gone? Sometimes the tricky little buggers don't even wake up if they know the milkwagon isn't on the premises.