Temperature & time necessary to carbonize all organics Suppose that I have a cast-iron pot which my awful roommate has vigorously scrubbed with soap and left to soak in soapy water over the weekend. The seasoning has been destroyed and replaced with awful-tasting soapy contaminants.

It seems to me that the simplest and best way to deal with this is to heat the pot over a campfire until only black carbon remains, then clean and reseason.

Not knowing exactly what is in my awful roommate's dish soap, and being a very fussy foodie, I want to be conservative here... so how hot would I have to heat the pot, and for how long, to be quite sure that virtually nothing but carbon remains?

Edit: Compare using the self-cleaning cycle of an oven for similar purpose, reported to work well...
There's a lot of exciting, and not well defined, chemistry that happens with seasoning cast-iron cookware.  Essentially, you are creating a cross-linked polymer film that is hydrophobic, providing a "stick-free" surface.  There are many many websites claiming the "best way" to season (or re-season) cast-iron cookware.  Few of these sites (and I'll let the OP and visitors search for those on their own) are based on science.  (Although I am not going to question tried and true family secrets, passed down from generation to generation.)  One site in particular makes a fairly convincing argument for seasoning that is science-based.  I suggest this approach can help restore your pot.

I suspect what has happened is that the scrubbing did remove the seasoning and exposed base metal to water and oxidation - your pot rusted.  The "soapy contaminants" is probably iron oxide rather than something from the dishwater, although there are such products as metal soaps which are metals chelated to long-chain fatty acids.

As for heating the pot to burn off all the residue - I doubt this is the most effective use of your time.  Scrubbing with acidified water to remove the iron oxide and a long seasoning session with an easily cross-linkable oil should get your pot back to (or better than) original condition.