This links to line 851 of MEGA_CoreStory_MAIN_MechaEncounter.txt where a lost in the battle of Element 5 of 'I Have Become Death' attempts to trigger the 'GoLoss' function of the first subplot of the Component with "Trigger0 .%id1%_%plotid1%_GoLoss". This is a problem since "CS_SubBossRoadblock" doesn't have a 'GoLoss' function.
Therefore, it is much more likely that line 851 should read "Trigger0 .%id%_%plotid%_GoLoss", which would make the line in the save "Trigger0 .3_1986_GoLoss" as above.
That means to get the game running again, all I need to do is type "Trigger0 .3_1986_GoLoss" into the debugger.
Side note: There is no reason that <I Have Become Death> should be able to redirect the flow of the script into one of it's subplots unless the subplot explicitly allows it. In this case, the parent assumed that the subplot had the function GoLoss, which it didn't, and which caused this bug.
Perhaps a plot should compile a list of all of its functions when initialized and then check when it is asked for one and return an error if the request can't be honoured.
Even better would be to force the parent to respect that it can only call functions that it knows about, either from a interface like overlay (all CS_SubBossRoadblock type plots will have a GoLoss function) or from being handed a list of what the plot allows during initialization (C style, I believe)