No, bits and bobs won't fly out! :I can't believe it's not butter! :I can't believe it's not butter! unless its well f@cked!
You can get spare engine casings, but they are VERY expensive. You can get aftermarket ones that are "protected" from damage in a crash, people like NRC do them
http://www.moto-racing.co.uk/Products/E ... sings.html
Normally its a case of draining all the oil, letting it sit for a day or so to make sure it is totally empty, undo the bolts, off with the casing, use a plastic scraper to remove all the old gasket (important it is ALL off and the surfcae is clean and dry), fit a new gasket, on with the new casing, new bolts with loc-tite preferably, torque them up, sorted!.
About an hours work at the most.