i know how you feel- i've just been on a 2 month trip over to europe and america with my family and didn't have a piano for 99% of the time (i managed to be able to practice on the baby grand in the hotel bar in lausanne, SUCH a nice piano, that was for about 5 days)- i was freaking out at the thought of not being able to remember my stuff, and i was still in the process of learning my pieces cos i'd only just started playing them a few weeks before we left, some vaguely memorised. So when i got back home it was really annoying having to semi re-learn all my pieces, though it wasn't as bad as i thought it would be- it came back reasonably quickly.
But, to top it off we were in the process of moving house when we got back to sydney, so i still didn't have a piano for a month after that, had to go practice at a friend's place.
But as for you, 2-3 weeks shouldn't be that bad, you might have to refer back to the music more, but if you do the whole mental practice thing whilst you're away, i think you should be pretty much ok.
tash