My H isn't a vanisher by the definition RCR gives, although he has certainly become more of one over the past two years. The kids hear from him once every couple of months, otherwise there is no contact.
I was just going to say that throughout this mess every now and again I would get "nice" texts or something, sometimes he even asked about how certain things were with me (health, relatives, etc.); I would respond thinking he was reaching out, but he always then ran again.
My own take is that he does things like that when he is either feeling guilty about something or thinks he "should", then completely forgets when his own life takes over again. I got the feeling that he thought he was being polite and "behaving how one should in these situations", but always at more than arm's length - the way you might with a distant cousin or so former university acquaintance.
He no longer contacts me at all; he now does that to the kids -- random texts every few months, the cynic in me says that he does this so that he can say "well, I tried, but they don't respond", in response to queries about his relationship with them.
As to asking for something; I agree that if it is important then ask, without any expectations. I have done so in the past, I've usually got what I've asked for (the request was always very specific, no embellishments or chit-chat), but there have been plenty of times when I've decided that it wasn't worth the contact and just not asked.