Does Egypt stamp vehicle details in your passport now?
My experience, albeit several years ago, was that vehicle details were not stamped in the passport, therefore if that is still the case, then you should be fine to leave the country without your vehicle.
The bigger hassle will be, as misterpaul points out, that Egyptian customs will usually only allow the vehicle in for the amount of time on your original visa. I understand it is possible to extend the customs paperwork in the country, but given Egyptian bureaucracy, this would be a nightmare.
The other option is to run the risk of not extending and then simply pay any excess when you leave. After my vehicle overstayed by five months, I simply turned up to leave at Nuweiba and payed the additional road tax before I could leave. It took an extra hour or so, but it wasn't a major hassle. There is a risk you might get pulled up at a roadblock on this point, but based on my experience, the police at roadblocks are far more interested in your passport.
I would be interested to hear if the roadblocks are still as prevalent (particularly in Sinai and the delta) as they were before the revolution?