This might be a slightly bonkers idea, SL, but here it is anyway. Have you thought of hypnotherapy to help you feel relaxed about your holiday? It's insufficient as a treatment for deep-seated issues, but does a brilliant job of getting you over a specific mental block. I used it when I had to go into meetings with my mad boss.
Now you've got a fairly clear picture of how your past is affecting your ability to enjoy the holiday, a good hypnotherapist can give you some tools to help you seperate "Lovely family time off in the sun" from the anxieties about runing away, risks and repercussions - the torments that feel all too relevant, but in fact have no connection with a package holiday at Xmas, iyswim. One or two sessions should be enough; ask them to teach you refreshers to take with you :)
Incidentally, if you've never done hypnotherapy (it makes you feel great!), look around at the other passengers waiting for the plane - can you see anyone pressing a thumb into the palm of their hand, fiddling with their ear lobe or doing deep breathing? Hypnotherapy 
Wrt to your other social events, can you try nurturing yourself through the process of getting ready and going to the first one? If plenty of time, planning, soothing breaths and positive self-talk can't get you happily through it, then you'll know whether to cancel the others. Please remember you can leave early if you feels stressed :)
Much to my delight, my DLA appeal was accepted so I should get a few hundred quid in backdates. I'm wondering whether to use it for the train fare to my brother's at Xmas, or to offer lunch at the pub with sister & family. Having said that, I'm in the middle of revising my relationships with all of them (in my own head) so this might not really be appropriate for me now. I appreciate your concern - thank you! Basically, though, I think this Christmas is going to be (yet another) compromise in the interest of my recovery. If I end up with Mum or sibs, I'll just behave politely - normal family Christmas in that case, huh?! And, if I'm on my own, at least I'll now have the cash to go to a pub for a bit of seasonal company.