How crucial is the transmission sensor?

My bf (the luddite -- so I'm online for him) has a 2004 wagon which developed a leak in
the sunroof, and the leak shorted out his transmission sensor. The cost to repair that is
not an option for awhile yet. He's thinking of taking the tranny sensor out entirely.

If it has an onboard computer that takes data from the gearbox and compares it to the
axle speed and does something with the output, this would probably mean Dead Car.

If it's one of the old types of engines that uses sensors for fun and perfection, but still
relies on mechanical engineering to keep things going, it should be fine. (I drove a truck  
with no accelerator solenoid for years.)

Which is it? Judging by the look of the engine, I'm guessing it's too fancy to work
without its transmission sensor. I'd like to be wrong. Thanks for any help!