What would happen to a Water/Lard Mix under pressure and high heat? If water is mixed with lard oil and heated (creating some super-critical water), how does this affect the volatility of the mixture in comparison if it is a pure mix of either water, or lard oil?

What happens when a mixture of lard oil and water is compressed and then heated to over 800 degrees Fahrenheit almost instantaneously (up to 1200 degrees Fahrenheit)? If it is in a well sealed copper container, would it be volatile enough to burst through the container?

Note: I'm no scientist or chemist, so use of laymen's terms, if possible, would be appreciated
I'm not sure what aspect you are asking about exactly… but all supercritical liquids are completely miscible with each other, so you would get one supercritical phase with the mixture of the two… supposing the oil doesn't decompose.

However, the smoke point of lard is 182°C while the critical temperature of water is 374°C, so what most probably happens is that your lard will burn, breaking down to glycerol, acrolein and free fatty acids.