Barely runs, no power, TCS off light, happened suuddenly

RE:My 2000 Saab 9.5 se V6 wagon. With 89,300 miles. Last major service was at 70,000, and included an ignition module
The car ran ok, until bringing my car in to replace the rear half of my exhaust. It was OK driving to the shop, but upon restarting to drive into the repair bay, there was NO power, & it barely idled. That's still the case after the repair. The CEL light was on prior to bringing it in, and still is, and the engine fault codes show misfires etc.
The mechanic checked to see what the codes meant, and checked out what he could, but did not know how to repair the problem. It's a reputable shop, but he's not a Saab technician.
I'm hoping it's just gone into Limp Home Mode, but.
Mike