If you buy-in for $100, make $200, then lose that $200 (which has to happen if you're eventually losing everything), how is it now more likely that you'll lose the other $100? I'm not really sure what you're saying.

The only effect that a large stack has in a cash game is that there is a greater maximum which you can risk on a given hand (up to the size of the second-largest stack, since you can't possibly risk more than that amount). This is really the only factor I can see which should influence your decision as to whether or not to cash out a certain amount.