Bottle sizes are set and regulated by the TTB, so a producer couldn't just start using 700 mL bottles. And to answer VAGentleman's question, 500 mL was dropped in 1989.
As far as handling shortages, different producers have taken varied approaches. Sazerac has taken a balanced approach: eliminate some products, drop age statements on some, and drop proof on others while maintaining age statements. Heaven Hill is a little more targeted, changing the Evan Williams line but not Elijah Craig, for instance. Wild Turkey... well, they're still trying to recover from the 1990s. A lot depends on how diverse your lines are. Sazerac has a lot products and thus a lot more options than say, JD. Maker's is the most extreme example, with only two expressions to work with.
Up until last week, Beam was largely immune to this problem, with the exception of Knob Creek a few years ago, which they managed to turn into a successful PR campaign. And really, they probably don't have a choice with Maker's, although I'll bet they're wishing they'd started that 3rd expansion.