I kept mine long - and I mean, hip-length - but only by sheer bloody-mindedness. :p I did NOT want to cave and get the "mom cut" - having long hair is part of my identity, as pathetic as that sounds. Unfortunately I was also doing water-only washing at the time, which wasn't as low-maintenance as advertised, for me. My hair got pretty gross without a lot of boar bristle brushing and grooming. So after a few months I switched to baking soda/apple cider vinegar washes, which made things considerably easier - and since then I've switched up to all sorts of methods, depending on the day. Conditioner-only, Indian herbs, however the spirit moves me.
Honestly, my hair (which is now longer than hip-length - I can sit on it) is a pain more often than not, but I like having it around for the days I actually want to do a fancy crown braid (a la my avatar!) or whatever. And it never looked good short when I was a kid, so I don't want to risk it. After this baby, I might get it cut shorter - like, back to waist-length - because it does actually make a difference in terms of feeling more low-maintenance, but I can still do all my hairstyles.
I always wear my hair up anyway, so baby-grabbing was never an issue. (DD does try to "help" me brush it when it's down, though - ulp!) Bunned or braided hair is really impressively baby-proof - whereas a chin-length bob has all these little tempting dangly ends that can't be secured without a good deal of fuss (cornrows? lots of gel? a really wide headband? I dunno!).
Also, yeah, hennaing postpartum sucks. It's a pain at the best of times, but I had pretty ghastly roots by the time I got around to hennaing after I had DD! Still, that's not a hair length issue... and I wasn't willing to give up my red hair. At least it was cheap and didn't require me to put clothes on and go to the hairdresser!
So anyway: I know PP haircuts can make some ladies feel like new women. But if you WANT to keep your hair, fight for it! :) Don't just chop it because that's what mums do - chances are you'll regret it, and feeling sad about that is the last thing you need post-partum.