1. Keep a roster spot for him anyway and wait for him to get healthy.
2. Release him and hope that no other team picks him up, then sign him to the practice squad.
3. Place him on IR and keep team rights on him, but shelve him for the season.
4. Release him and hope no one picks him up and wait till he recovers from his injury to resign him.
Of course the Saints could also just get rid of him, but let's work under the assumption they want Morgan based on the value he brings - I think that's safe. The least likely of these scenarios is probably #4, because most of us have the sense to believe SOMEONE will give this kid a practice squad spot at minimum based on what he's shown in the preseason even with his injury. I also think #1 is rather unlikely because I don't think 2-4 weeks is an accurate assessment of how long he'll be out. He may be "back" as in practicing in 2-4 weeks, but with a meniscus tear there's no way he'll be back to the speed he was prior to the injury by then. If you remember, this is the same injury that Hornets' star Chris Paul had and his speed was never the same after the injury. Now Chris Paul is so good and such a superior athlete, he was able to perform at a pretty good level despite being hampered by the torn meniscus, but unlike Paul, Morgan hasn't shown any other attributes besides speed yet. What we all like about Morgan is we've seen explosive speed and game breaking ability. It's going to take more than 2-4 weeks to regain that kind of ability, trust me. So keeping him around is being waseful with a roster spot and the Saints are already quite banged up.
So that leaves us with... either placing him on IR, or releasing him and putting him on the practice squad (assuming no one else picks him up). I think those are the two most likely scenarios. I do think it's unlikely another team would give a guy like Morgan a 53 man roster spot based on his torn meniscus. It's a risk, but one I believe the Saints would win. I do believe many teams would love to have Morgan on their practice squad, so the Saints would also have to hope Morgan agree to stick around. Probably a safe assumption. If the team places him on IR, it's safer in that they guarantee he'll be a Saint in training camp next year but it also completely handcuffs Morgan and ends his season. I could also see this happening because the Saints may feel like they're in a good spot this season with receivers. It's a deep position with Colston, Moore, Henderson, Meachem, Arrington and Roby. Perhaps Morgan would be more useful to the team next year if the Saints don't have the same list of players. It's really too bad this happened to such an exciting player, but to say his place with the Saints is in jeopardy and perhaps even his entire season would be an understatement.