Wut? Only Steam would need to be "Cracked". They'd just remove Code from Steam that does a Check or add a Null Server that returns an OK back.
this x2 and it has already happened.
Before i went bonkers on steam games(have over 200 now) I downloaded a cracked steam client just to make sure that i had a out if valve ever did go under, and on the 5 games i tried they all worked on the cracked steam client. So its not like you dont have options if steam does ever go away, im sure some of the online aspects/servers/community will not work on a cracked client but i consider the price of most steam games(only buy games on sale) low enough that if i did lose a few online features it would still be worth it. my .02