I have to say that I am baffled by the problems a few folks reported about removing and reinstalling a RD. I have removed mine for packing a number of times and it never took more than a few minutes to reinstall. I never even had to touch the adjustment. Shift the shifter to the loosest position and there is usually enough slack, but if there isn't as you mentioned just pop the end of the cable housing out of the braze-on on the chain stay. That will allow all of the slack you need. Then pop it back in once the derailleur in on.
I do think that it is smart to have done the operation before and be familiar with it before relying on doing it on tour.
Oh, and if adjusting a rear deraileur takes more than a couple minutes you should probably bone up on that as well. The limit screws should not need to be touched once the bike has been set up properly for the first time. So the only adjustment needed is cable length. On most of my bikes that is most easily set by shifting the shifter to where the cable is loosest and with the chain on the correct cog adjust the cable so there is just a tiny bit of slack. Worst case it might still need a 1/4 or 1/2 turn on the cable adjuster if it isn't already perfect. If you have adjusters on the head tube you can even tweak that while riding.