Measure the off resistance across the FET (source-drain) in the IRF7413s? At least to compare against the new ones you've already ordered before soldering replacements in?

From what you're saying I'd probably be blaming the MAX1631 actually. i.e. it's gone a bit mental and turned on both FETs resulting in essentially a dead short on the input supply.

That said the heat from the "induced" short may have since killed the IRF7413 chips.

I don't know if there's anyway you could diagnose the MAX1631 whilst installed with no FETs. I would expect the "top" FET would be turned hard (since the controller will not be seeing any output). At least I'd expect the "bottom" FET to be off in that situation.