It is very difficult for Manchester United to get into the top 4 places. Considering the tough rivals in the Premier League along with the point difference, I think it would be better for the league to fight to get to the European league. They had some good games against the best teams in the league, but considering the poor performance in the UCL this year, it was not the year they wanted at all.
That is not going to happen, at least I have to say I would be shocked if somehow ten Hag manages his team to achieve the top four, but as of now I would rule that possibility out at 99%. I don't know what would have to happen in order for them to climb up the table, but Manchester United is still facing Liverpool and Arsenal and some other pretty good teams. I doubt that now out of a sudden they turn into a top team and win most of their games. Even then it may not be enough as they are 9 points behind. Last season they somehow did it, but not this time.
The problems of Manchester United is inconsistency. The inconvenience might be attributed to unavailability of Manchester United players due to prolonged injuries. Erik Ten Hang has never had a handful of players available for him to choose. If defenders are available today, midfielders will not and if midfielders are available, strikers will be lacking. So, I applaud Erik Ten Hang for using an inconsistent team to go this far.
Manchester United might not be able to qualify for the top 4 this season but the management will have to buy new players for the next season in order to fight well.
But the problem that ten Hag didn't have that many players available as you are saying is not only because they were suffering from injuries all the time. One of the biggest reasons was that ten Hag scared away some of his players and made them leave the club again before they even arrived while others were ruled out by principle more or less. When ten Hag doesn't like a player, it is almost impossible for that player to ever get a fair chance to make it into the first eleven of the team. His approach sometimes seems to be too ideological in my opinion and he has an alpha male complex. He wants to have control and to prove to the whole world that he can discriminate against any player he wants because he is the boss. He is one of the worst coaches out there in my opinion.