Justine, you might be surprised hun. DH left for a four month stint when DD was 18ish months. She is a daddy's girl and I was terrified of how she'd go.
They have NO concept of time/days/dates. When she'd ask, I'd tell her he was at work and would be back soon. SOmetimes he has to work away. They fact thet mine is a shift worker and already works differing shifts all the time helped a little I guess. She'd talk to him on the phone - so he was still 'around' in her mind and it was all good.
I also used to tell her (and got DH to in the time before her left) that Daddy said I (me) needed to do his special jobs until he came back. She was cool with that.

Good luck.