My friend has a 2002 496 Mag HO with 725 hours. He's never had a problem with it and therefore has never had any work done to it (ie top end rebuild).
A couple weeks ago he "winterized" his boat to me it was basically like doing nothing...He drained the block and changed the oil! No fogging, no fuel stabilizer, no antifreeze etc.
My question is how much damage is he doing by only draining the block? Isnt he asking for problems doing this basic winterization when his boat has 725 hours on it?

A 496 should have antifreeze in the block.
normaly you should drain the exhaust and run coolant through it and check/change the block antifreeze. stable/additive SHOULD ALWAYS be use with this crappy gas we have.

He is risking issues, but not guaranteeing anything.

He is risking internal corrosion by not fogging. He is risking having bad fuel and fuel-related problems by not treating.

He might have been lucky for a while, but I wouldn't skip what he skipped.

i have always flushed the motor and anything that has water running throu it. disconnected the batteries and thats it. if its only for like 4-5 months ,ive never seen fuel go bad in that short of time. i never fog the motors. i store cars for over a year with out fogging. no issues there. maybe i got lucky for the past 15 years but i doubt it.

Like was said, 496ho's have closed cooling with anitfreeze/coolant in the engine. They don't need to be drained. He is probably draining the water out of the heat exchanger and exhaust.
I never fog my engines. I always add Stabil to my fuel.

No fogging here either, always just fill with antifreeze and add some stabile. Yrs ago when I'd pick up a junk motor for parts, whenever I tore it down, the inside has always been 100% rust free as long as it hasn't been sitting with the heads off. Then they'll rust fast.