Here's my prediction:
1. Yes, his stock was starting to tank based on his play before he went down, but it was such a small sample size that it could be attributable to a slump, bad puck luck, poor play around him by others, hidden injury/illness that he was playing through (even if he wasn't really injured/ill, the Ducks could be told that he was to help his cause), bad coaching, etc. The Ducks have seen him at a number of their own camps by now, so they know what he can do (e.g., the viral video of his ridiculous goal at camp this year).
2. There is zero chance of him coming back next year. From a hockey standpoint, he should not have even come back this year, but he wanted his degree and he wanted it paid for by his scholarship, so it was a life decision, which I applaud. However, once he gets his degree, he is gone - there is no reason for him to return.
3. The better question is whether returns at all this year, even if he is fully recovered from his injury. He can control that process with the medical staff and it will be interesting as to whether he wants to gamble on his future by playing again this year. Personally, I don't think he has anything to gain with the Ducks, so he may not come back unless the Ducks have whispered to him that there is no place for him in their organization. In that case, he may come back to impress other teams. But I really feel he is already a known quantity at the NHL level, and teams either love him or think he is limited. Perhaps he wants to put on his cape and try to bring home a Beanpot trophy. I guess we'll see.
4. Derick will be back for sure. The family has already shown that it values a free education, so why not let the less talented son suck up as much free education as he can.