One of the frequently asked questions about the previous few parshiyos is: Why didn't Yosef HaTzadik write home?
Recall that Yosef's time in Egypt was not spent in altogether bad conditions. Other than a few years in prison he actually lived quite well. For the first few years he served as major domo for an important Egyptian official, Potiphar. After being released from prison he served as major domo to Pharoah himself. During his time in both positions he would have had ample opportunity to send a message to his father as to his whereabouts but there is no record in the Torah that he did.
Now there is the classic answer from the Midrash, that the brothers made him swear he wouldn't but (and perhaps I'm succumbing to personal bias here) I always thought that such an oath would probably be disregarded once he was out of danger. On the other hand, the suggestion that he didn't send word because doing so would have ripped the family apart when Yaakov Avinu figured out what had happened does sound plausible.
I would like to suggest two further possibilities.
One is quite practical. Let's say that Yosef, now a servant of Potiphar, sent a message to Yaakov Avinu. He could have been discrete, saying that while on his way to his brothers he was kidnapped and taken down to Egypt. This way he could explain his current situation without implying that his brothers had been complicit in the process.
But what would the outcome have been? Without a doubt Yaakov Avinu would have sent down some or all of the brothers (sans Binyamin) to either buy his freedom or rescue him in some other fashions; the same brothers who - unknownst to their father - sent him there in the first place. Could we really believe that Yosef, having been freed by Potiphar and handed over to his brothers, would happily walk off into the empty, lonely Sinai with the same brothers he had such bad memories of? There's a matter of trust to consider. So perhaps that might explain why he didn't send a letter. There was no practical way to get home.
But here's another consideration. Yosef, we are told, subjected his brothers to the torments they suffered from his accusations because he wanted to bring his dream of the 11 of them bowing down to him to fruition. The only way to do that was to convince them that he was powerful and to get them to bring Binyamin down to Egypt. As we see from recent parshiyos he was successful. The 11 brothers all bowed down in sincerity to him. Fine.
But recall that Yosef had a second dream, one in which his brothers bowed down to him along with his father and mother. After all the effort he put into making the first dream come true we find no record of the second dream coming to pass. Or do we?
Chazal tell us one of the suspicions Yosef had when the brothers promised to bring Binyamin to him was that they would grab some no-name from the Egyptian market place and present him as the youngest brother. This was certainly a fair concern. Yosef had left home when Binyamin was still quite young and frankly, if the brothers couldn't recognize him because he was older and bearded, how could he be sure that he'd recognize Binyamin after all this time?
The answer might be from something Yaakov Avinu repeatedly says throughout the narrative. Binyamin is especially precious to him, remember, because he's the last child from Rachel Imeinu, his favourite wife, now that Yosef is gone. Chazal tell us at the beginning of VaYeshev that Yosef's face was similar to Yaakov Avinu's. Could it be that Binyamin strongly resembled Rachel Imeinu? That would serve two purposes in this story. The first is that his presence would be a constant reminder to Yaakov Avinu of Rachel Imeinu. The second is to allow Yosef to recognize Binyamin. He would certainly remember what his mother looked like, after all.
The final peace in the puzzle in Yaakov Avinu's blessing to his sons when they take Binyamin down to Egypt. At this point the narrative depicts him as a broken man. When he was about to meet Eisav years earlier we saw a very different Yaakov Avinu. He prepared for that confrontation through prayer, gifting and preparation for battle. Here he simply asks God to have the unknown Egyptian rule show rachamim, basic mercy, to the brothers. No demands, no threats of bringing down Divine wrath if Shimon is not released or Binyamin doesn't come back. Just simple mercy.
This therefore would seem to be the fulfillment of the second dream. When all eleven brothers bow down before Yosef, Rachel Imeinu is present through Binyamin acting as a reminder of her and Yaakov Avinu is essentially bowing down through his request for mercy. Thus the second dream also comes true.