Though BioWare, the developer, has already cleared that players will not be seeing their favourite character, Commander Shepard, the human protagonist in Mass Effect series.
However, if the company wants, players are likely to get a chance of seeing their favourite Mass Effect character in the yet-to-be announced video game Mass Effect 4 (the game is sometimes just called the Next Mass Effect). A report from Gameranx discusses the possibility of Shepard reappearing for one last time in the Mass Effect 4.
Given the past statements from developer that says players will most likely see some of the companions of Shepard in future. This brings us to the question of why not Shepard himself/herself.
It will not be the first time in BioWare's games that we see a returning protagonist. In Dragon Age: Inquisition, players meet Hawke, who was the protagonist in the developer's earlier game in the series, Dragon Age 2.
It goes without saying, the amount of disappointment that players felt when Mass Effect 3 ended. But it could be possible that the company might let him/her make a comeback for smaller role where players can 'say their final goodbye.'
Even if Shepard does not come back in person, he/she cannot go without being mentioned in the next Mass Effect.