Originally Posted by redondoaveb

If you break a cable on the rear derailleur, you can rig it up to stay in one gear if you're mechanically inclined. If not, it defaults to the highest gear (smallest cog). If the battery goes dead on the rear derailleur on electronic shifting, you can use the battery from the front derailleur which doesn't get as much use as the rear and should be pretty much fully charged. That is, if you charged the batteries before you left.