Jackett’s side opened up a 2-0 lead through Nouha Dicko before Aiden O’Brien reduced the arrears at Molineux on Saturday.
Ethan Ebanks-Landell put Wolves firmly in control before Lions substitute Jamie Philpot scored with his first touch in senior football, only for Sako to give the final scoreline an emphatic look in stoppage time.
Talisman Sako also set up two goals, but the Mali international is out of contract this summer and reportedly being courted by top-flight clubs in England and overseas.
Jackett said: “I do fear that could be his last game. From the board’s point of view, I do feel that they did very well to keep him through the last year of his contract. It was a big commitment from the chairman and the board and they should be commended for that.
“It does look like he will have offers from both home and abroad that will tempt him. He has been a good player for me and I felt that it would be a big finish for him. I could sense that, and that there would be some goals and a big effort. In terms of a talent, he is a good all-round footballer.
“He knows that we would like to keep him, but to be honest it does look unrealistic.”
Jackett put a brave face on coming so close but missing the play-offs, and thinks it bodes well for the future.
He added: “Before the game we knew that getting into the top six looked possible, not probable. We needed quite a number of teams to slip up and we knew that it would be a long shot.
“But we had to keep our eye on the ball and win the game, and it was a good performance. I was very pleased with the players.
“Things didn’t work out for us but we wanted to send the fans home optimistic for next year.
“We are disappointed not to have got one of the three promotion places and I am sure that we will analyse things and look back at November when we didn’t get a point.
“But overall it will be a good season if we can build on it next year. Everyone has to be hungry enough to get better.”
Millwall boss Neil Harris, who was unhappy with his side’s defending, has promised that there will be a major overhaul of the squad this summer as he sets about planning for a future in League One.
“There will be discussions with players regarding contract situations,” he said. “We have got over 20 players out of contract and there might be a couple that will be in my thoughts for next year. But there will be a hell of a lot that won’t be.
“I am crystal clear where I want to go with the team. I know what it takes to play in front of our supporters and what makes a good Millwall team and I know exactly the characters that I need in the team and the mix between youth and experience.
“The biggest thing is we are not accepting what has happened this year and saying we will go down, rebuild and go again.
“Of course that is the aim, but at this football club there has to be a winning mentality.
“I think the players saw my frustration and after the game I let them know that I wasn’t happy.
“We let four goals in and that is not acceptable. I think you saw today, with three in the team and two coming off the bench, that the young players at the club will be given an opportunity.
“They will grow as a group, not as a sacrifice to results, but if it takes them time to come through – as it did when I came through – so be it.
“We look at Wolves as a model and how they played in League One last season and use that as an example.”