Question: If the active player ends up losing characters to the terror or combat struggles and no longer has any character committed to the story, does the opposing player continue with resolving the investigation and arcane struggles? Or, does the story card immediately stop being resolved because the active player no longer has a committed character?

The rest of the struggles still resolve.

 I see no reason to stop resolving stories. (i might be wrong on this though)

There are two rules in the FAQ:

1)Stories will resolve only if the active player has characters at that story.
2)Additionally, if a story card is won by any player before it is resolved (i.e., at any point during the story resolution sequence), all success tokens are removed from the story, and all characters are no longer committed to that story. Any remaining steps of the sequence are not resolved.

2nd is certainly not the case here, but worth noting

1st is a bit troublesome for me as it doesn't say when exactly is this condition checked, and some things happen during commitment and resolution; but i still think it specifies when story resolution starts, rather than a condition that needs to be maintained for story to continue resolving

at least i never stopped resolving a story for this reason, seems weird to me (still with game of this complexity and rule clarity its not hard to be wrong, and here i see room for other interpretation)

 Thanks for the replies. We resolve stories all the way, but I have never seen any rule that definitively settles it for me.