Pancake Lens or Sony RX100 for Travel?
40mm is a pretty awful only focal length on 1.6x crop. That works out to, what, 64mm equivalent? So you'll be able to take some nice short telephoto shots and some portraits, but good luck with scenery. I think it would be horrid for travel.
Also, the camera is fairly good sized. Shaving a couple inches off the lens isn't really making it more portable. You aren't going to fit it in a noticeably smaller bag or a coat pocket by switching to that lens.
I'd say T1i and a versatile zoom, or something that is actually compact. Maybe the Rx100. The GX1 kits are only $599 now. XZ-1 just dropped a little in price.