Firstly, Lava, let me be blunt. Your sarcasm really bothered me. Secondly, Aslan was not Peter's 'last resort.' At least not how you mean it. I believe that Peter looked around him and noticed that Aslan had not come, and he had the opportunity to come. Honestly, while I understand why he did not come sooner, I can understand how anyone might wonder why he had not come back. Peter was observing the situation and realizing that Aslan may not come anytime soon. In the end, he realizes that he is wrong, and that Aslan had come, he just had not shown himself yet. Remember when Peter bows to Aslan in the end. I believe that if he did not believe in Aslan, or just saw him as a 'last resort' he would not have bowed.
Now for Miss Reepicheep. I am so sorry, but I disagree so much with you that I do not know where to begin. I do not see how you DO NOT SEE HIS CHANGE! When he says "We are not really needed here anymore." I feel that he said it in a "You're right, I am not needed anymore. Caspian can take care of the country I love and would sacrifice my life for, and Aslan will always be there."
I believe that Aslan would not have let Peter go if Peter did not believe in Him anymore, or did not have faith in him. And Peter was VERY HUMBLE IN THE END!!! I realld do not see how you do not see it!!!!!
Remember, both of you, that he cared about Lucy very much, and would not have sent her out into the worst part of the forest in search of someone who he did not believe was coming..