Shariputra and a bodhisattva losing bodhicitta In my copy of Shantideva's Bodhicaryavatara, there is a footnote referencing a story about Shariputra losing bodhicitta.  Apparently a demon asked for his right arm, Shariputra willing gave it.  But the demon is offended that Shariputra offered it with his left hand, at which point Shariputra dispairs.  According to the footnote, this story is told in the Lotus Sutra.  But, I cannot find it there.  (Granted, I do not have complete version of the sutra to search through available to me.  So perhaps it's in the missing material.)

But I also have a vague memory of another story about a bodhisattva losing bodhicitta.  The story, as I recall it, recounts how the bodhisattva works tirelessly to save all hell beings and at long last manages to liberate the last being from hell.  Hell is empty.  Having completed his work, the bodhisattva lets out a sigh of relief.  And, in that instant, hell is completely repopulated once more.  The bodhisattva grows despondent that his efforts have been to no avail.

I've tried a web search for this last one. While, not surprisingly, I get many hits on bodhicitta, I haven't found this particular story.

So, I have three closely related questions.  Where in the Lotus Sutra does this particular story about Shariputra's loss of bodhicitta occur?  And, who is the bodhisattva in this second story?  In which sutra(s) can this story be found?
I can only answer the part of your question relating to the Lotus Sutra. I hope a partial answer is better than none.

From my recollection of reading the Lotus Sutra - Shariputra is portrayed as someone who hasn't made the journey all the way to enlightenment yet. He believed he had however the Buddha clarified this and states that he is stuck on the lower teachings. Unlike some other Mahayana sutras he is portrayed in a positive light and it is predicted that he will attain full enlightenment and become a Buddha named Flower Glow.

Though it isn't translated as bodhicitta in my copy I think this might be the quote you are looking for 


  Shariputra in the past I taught you to aspire and vow to achieve the
  Buddha way. But now you have forgotten all that and instead suppose
  that you have already attained extinction.


[Quote from pp 51 of the Burton Watson translation]

I read 


  vow to achieve the Buddha way


as the bodhicitta - which I have previous heard translated as the 'will to enlightenment' which I propose is the same thing.