"NASA has not said what will happen if the weather is still looking bad by the time the second landing window rolls around,"
Yes they have. The Shuttle will stay in orbit until tomorrow and try again.
Friday allows four attempts. Two in Florida and two in California.
Seven possible landings on Saturday. Two in Florida, two in California, and three in New Mexico.
The Shuttle can stay in orbit until Sunday, but short of a serious emergency, it won't happen.
If they can't land in Florida today or tomorrow, I expect it to land in California tomorrow.