I think it's fine if he's a lovely dad the rest of the time and you've got lots of celebrations to get on with. I assume they can do something when he gets back. Don't let it happen 2 years in a row - that would be wrong!
I missed my DD's 6th birthday as I was working in Uganga at the time. She was fine about it, we had a party for her a month early before I went out. I wasn't even getting paid - never mind £1000! I think it'll be fine.
Dh was often away for ds's birthday and being Armed Forces, there wasn't much we could do. He always phoned if he could, and we had a party when dh was home. I cooked whatever ds wanted for tea, and when he was at prep, they always made a cake and celebrated with his class at break time.
DD was 4 this year and it's the 1st time DH has been at home on her actual birthday.
I usually take her out for a meal with my parents on the day itself and DH always makes sure he's around the following weekend for birthday party, and takes her out somewhere nice in the morning while I get the house/food sorted.
If it makes you feel any better, my 5 year old finally got her "birthday treat" of a day at the zoo 3 weeks ago. Her birthday was in February I do think birthdays should be special for kids, but sometimes a bit of juggling is necessary for the sake of the family!