How Shepard can come back in a mass effect 4
If you chose pick to unite synthetic and organics or destroy sythetics in Mass effect 3 then Shepherd might be able to come back.
My idea is that Shepherd when he jumped in to the beam catalyst put a under armour over him so that he doesn't die. He was put into a coma the catalyst downloaded itself into the armor and and shepherd with nutrients over the course of a few months when he landed in a wasteland on Earth Shepherd finally wakes up and the catalyst sets up a distress beacon. After a few hours Kaidan and a team comes to investigate. It turns out kaidan has been helping rebuild Earth over the past few months everyone in the milky way slowly gets word that Shepherd has been found alive on birth and the Normandy decides to fly in and see for themselves it turns out kaidan has been put in charge of the Normandy since Shepherd was assumed ded. Kaidan very quickly puts Shepherd back in comand of the Normandy and Shepherd goes to meet the council or whatever government figure they have right now. Shepherd learns from thembut there has been a lot of tension because the krogan and the quarian are both trying to get back land that they used to own this creates a lot of tension and it seems like everyone is about to break into a galactic war. This is how I would start the story of Sheppard coming back
I would also make shepherds new armor adaptable and let it be fully costamizable.
