I still nurse my nearly 4 yo to sleep. When ds2 arrived, dh and I did tag-team parenting. I would nurse ds2 to fill him up, then I would nurse ds1 to sleep while dh walked ds2. If ds1 did not fall asleep in a reasonable time and ds2 wanted me, then dh lay down with him while I took ds2. Ds1 was also not night-weaned, although he usually slept through. But, if he woke up he wanted me. But if ds2 was already nursing he would have to wait. If he could not wait quietly, then dh would take him back to his bedroom (usually screaming). I would go to him and nurse him if I could, but often I was occupied with ds2 until after ds1 cried himself back to sleep (in dad's loving presence, not cio). Eventually, ds1 asked for dad when he woke up, and would fall back to sleep for dad. Now he is going through a phase where he comes into bed with us and MUST sleep next to me. But, he no longer asks to nurse when he comes in. He just crawls in and goes back to sleep. Meanwhile, ds2 actually NEEDS to walk around with dh for awhile to fall asleep... but, it's rare that dh can put ds2 down and have him stay asleep, so then I nurse him back down. But if I try to nurse him to sleep before he gets his daddy time, it doesn't work.
Ds1 can fall asleep without me, he just generally doesn't choose to. A couple of times he stayed the night at his nana's house (his idea) and went to sleep fine with nana. But, otherwise, he insists on waiting for me... even if nana's babysitting at our house.
It was tough for awhile, but things've worked out, and dh being forced into taking on more of a night parenting role has been good for our family as a whole.