In this situation, what could Herrera have done short of fouling Bruma? Bruma passed the ball to someone else and ran past him. This is called a one-two pass in football. Only way Herrera could have stopped that is by fouling Bruma as he runs past him, which would result in a yellow card in a competitive match. It was a good offensive move, that can be stopped if the defenders react to it. Blind was the free defender and didn't react to it, hence the goal.
I think Herrera is an average player with good potential due to his jack of all trades skill set. Some people over criticize him while others overrate him. No need to call Herrera out for bad defending or a lack of effort when he runs around the pitch with 100% intensity making tackles. You can criticize his passing during this game which was safe and mediocre. He needs to make those risky, game changing passes we saw in the 2014/15 pre-season and during his time at Bilbao. LVG has hurt his progress as a player with forcing him to change his game to make safer decisions with passing/positioning. Unless he can get rid of that, he won't make it under Mourinho and as a player at the top level.
He shouldn't have been on his back foot in the first place i.e either keep moving or having his body sidewards to anticipate a dribble/1-2 etc. I haven't seen the replay again but he was caught by a simple 1-2 on the edge of his own penalty box. It happens all the time in a game but unfortunately to him it lead to a goal.
The problem in the first half was that he was too far away from any of other intelligent players (Martial, Miki, Zlatan..basically anyone but Rooney) where he could play 1-2s, get involved in link up play etc. Add in in the lethargic pace it was a recipe of disaster for any midfielder of his ilk.
Interestingly though, in Mourinho's post-game interview, he mentioned that he told the players to not care about playing up to the speed of the game and just get minutes and feel comfortable on the pitch (referring to Martial, Rooney, Schneiderlin, De Gea etc after only training for 2 days). So maybe the players didn't push the tempo because of that.
In Rashford's interview, he said Mourinho told them to close the space and well, we saw what happened when we did.
Anyways, I'm a big Herrera fan simply because it's nice to have a midfielder, who can control the ball in tight spaces, not be scared of a press, is intelligent with his link up play AND can move around the pitch with physical purpose (i.e that rules out Mata). I'd love if we can have an actual midfield 3 and be able to control games without needing to resort to being compact and disciplined when we play against the cream of the crop.