When do industry experts expect that traditional paper maps will
become obsolete as they are replaced by online maps and GPS
navigation?  I am interested in folded, paper maps, not decorative
maps for walls or antique maps.

Ideally, I would like to have a specific estimate (ie. sales of folded
paper maps will decrease from X to Y in the next 5 years). If that is
too hard to find, a trend would be useful (ie. what % of people in the
US no longer use paper maps and how is that trending).  Thank you very
much!

Paper maps will NEVER become obsolete. All the electronic methods of
navigation will always have to be backed up with paper maps (and a
simple magnetic compass). Satellites can be affected by weather, etc.
Electronic navigation systems require an power source (batteries,etc),
which can fail.

Imagine getting on a long flight that loses all electrical systems,
with no map backup, it would probably end up being your last.

Never is much too long. While I agree there will be a nich for paper
maps for back up purposes for the rest of this century, look for a
very slow decrease. I would say, rapid decrease except, twenty years
ago, 90% of the world's population had poor to negligible map reading
skills. Thanks to computer maps, the number of map readers has likely
doubled and will continue to grow. Some of these people are
discovering the conveniece of paper maps.
 GPS however is costly, complicated, another gadget to carry, charge,
and malfuntion. My guess is 99.99% of the world's population will not
have instant access to GPS at this instant in 2007. By instant, I mean
how many seconds would it take to get GPS information, if you just
woke up in bed? After 2007, a new generation of GPS like devices is
likely to cut into the market for both paper maps and computer maps. 
Neil