It is just really difficult for Manchester United to achieve this comeback with Erik ten Hag as it seems. Because there is still no sign of any recovery. They just continue to lose points which caused the gap with top four to go up to nine points. There are three teams between as well so it is very hard for Manchester United to make it to the Champions League again.
I think this must be an enough reason for the board to sack him by the end of the season at worst. If they were a title contender in the previous season then maybe Erik ten Hag would have still had a chance to stay longer even if he completes this season poorer.
Do you mean comeback to the top 5 in EPL standings? You're right, it seems very difficult to return to the top 5 because Man United performs very unstable and the point gap with Tottenham in 5th is quite large. If there is no change with Man United, I think Man United probably finishes in the 6th place for this season. However, it won't be easy, West Ham and Brighton are competing for the same position. Man United also must be aware that West Ham and Brighton aren't weak teams.
Yes, it is time to fire Ten Hag. After this season is over, I am sure Man United probably fires Teh Hag. He failed to improve Man United, he also made some problems with players. It is not a wise decision to keep Ten Hag in the club if he often makes problems.
It is very difficult for Manchester United to return to the same position as last season, maybe last season Manchester was still lucky because they had players they could rely on. If Erik Ten Hag didn't make a change in players, maybe Manchester United could still maintain its performance with the players they had before, but unfortunately because Erik Ten Hag made several efforts or changed players, it actually caused Manchester United to decline. And worst of all, Erik Ten Hag couldn't do more with the players he recruited his coaching strategy really failed this season.
Yes, it is possible that Manchester United's management will maintain it until the end of this season if there is no good improvement, why keep a coach if he is not able to provide better, it just gets worse, there is no other reason not to fire Erik Ten Hag because this coach really has too much problems within the club, keeping him will only further worsen the club's condition.
I guess the top 5 position are already set and there's very low chances of it being changed. There would be competition for the positions within the top 5 but I don't see lower teams in the table replacing them. Though there are 18 matches left for most teams, there's nothing that could drastically change how they are performing. There's a 5 points difference between Tottenham and West ham, which may seem small but while distribution on matches needs a long time of favorable results to change. There's no way for Manchester United to get on top 5.