Oh dear, I really feel for you. I was sort of in the same situation.
My folks were in Turkey my sister was at least 2 hours away. I did have local friends who said they would take my oldest if I wanted, but they all had children of their own or were working (and as you never really know when it's going to be, it's hard to make firm plans¬!)
I decided that my sister would have to come.. and I would call her the min I had a show and twinges. However, what happened in the end was my sister bailed with the weight of responsibility (I don't blame her for this), and we both asked my folks to come back from Turkey to be on standby for us. I had a show about 10am on the friday baby was born.. called my folks and told them to take oldest about lunchtime. I had a gut feeling it was going to be that day. Baby was born about half 9 at night - so loads and loads of time! and also there was no need for oldest to leave really, as she woudl have been in bed at the time.. but I somehow felt more at ease with her out of the house, least of all so I didn't have to be mummy with her (selfish I know - but sometimes we all have to be ;-)
Rack your brains for family that will be there for you - they are usaully the ones that in a fix really will move mountains for you!.. and if your lucky enough you can make some back up plans for staying at home with you or for going away, or if you transfer into hospital (worth thinking about, even if it is for a short while.
It doesn't help to say, I know as I had it said to me.. but things always work themselves out - esp when you get emotional and desperate! ;-)
Xxx