If your gynae is travelling she will have someone else handle all her patients. The hospital will be informed so that when you arrive they will advise the other gynae. If you definitely want your gynae to be there then you can only make sure by having planned c section.
The piles - I developed one (which I called 'my friend') before giving birth, it wasn't too bad though gave me some discomfort made worse by the extra stomach weight. It went away just before I delivered and came back with more friends after delivery.
If you feel strongly about a natural birth then give it a go. Yes the piles may get worse but they can get fixed. Honestly whilst you're pushing the pain of the piles is not even felt. Afterwards there will be discomfort but I think the hospital also offered me some oral medication for the discomfort.
I would maybe talk to your GP a bit more about possible treatments, cost and recovery time if you decide to go natural and the piles get worse.