How much pressure can a flip top take? I'm making mead, 3 lbs honey topped up to 1 gallon with champagne yeast. My final gravity is ~1.044. Still lots of sugar in there, but fermentation had all but stopped. I put it all into 1 Liter flip top bottles. Here's the question: have I just made bombs? How much pressure can fermentation-grade flip top bottles take? 

I know 1.044 is still kinda high; I don't need a lecture. I don't think that fermentation will start again, but if it does and this stuff pushes itself dry, how much pressure will that make, and can the bottles handle it?
The short answer is - "It depends, probably not".

Bottles are usually rated for Volumes of CO2.

Champagne bottles are typically rated for 7 volumes.
Wheat beer bottles should take around 5 volumes.
Ales/Lager beers are normally carbonated at 2-3 volumes.

However, flip-top bottles (I assume you mean the ones with the rubber seal) are produced in both CO2-rated and cheap un-rated beverage bottles - found in supermarkets.

As you say 1.044 is quite high - plenty of beers start around that point.  This could generate a lot of CO2 (> 15 volumes) if it fermented out.

The actual CO2 volume calculations are discussed in another answer.

It might be better to transfer the mead to PET(plastic) bottles, and store them in a safe location.