Do you mean the black plastic acoustic cover that covers the engine and is secured with 3 bolts? If so, Stanleysteamer is spot on, just take it off and carry on driving. It does nothing but hide the engine from the non-mechanically inclined, and supposedly reduces engine noise. Many people don't bother with it at all.
If you mean the aluminium "rocker" cover with the yellow oil filler that gives access to the injector harness, then I would be more cautious. With some areas unsecured there could be potential for warping if you drove it for a long period. I would consider it driveable with caution, but I would want to remove and replace the snapped bolts asap.
In the meantime, keep the faith and follow Sierrafery's advice.