I'm not quite sure what a valet key is (don't have them in Europe!)

If you have the electronics in the original key still functioning then
the second key can be programmed off the first key (but you need a Saab
dealer - or perhaps a GM dealer will have the equipment).  The problem
arises if you loose all the keys to the car then that means a huge
wallet emptying exercise as big chunks of the security system have to be
replaced.

You might be able to get the car to start by using the 'valet key' in
the ignition and holding the broken key next to the ignition switch as
the electronics to read the key are part of the ignition switch and read
the key wirelessly. Or, if the keys are the same (my 9-5 has two
different shape keys) then swapping the electronics over is relatively
easy giving you one good key)

Hope you get going and don't forget to get a second key programmed as
quickly as possible.  Can you buy Saabs in Mexico?

You can check how many keys/transponders are programmed to the car by
pressing the boot/trunk release button on the key whilst the engine is
running, the SID display above the radio will tell you how many keys the
system is programmed for.

Andy