Other mistake: So let me get this straight: Optimus Prime has Energon Swords hidden in both of his arms, with which he can slice through an entire Decepticon in one chop, yet when he is hanging from a few wires, despite having one arm entirely free, he can't cut himself loose?
Factual error: When the Autobots return to the moon in the present day to retrieve Sentinel Prime, they pass by the Apollo 11 lunar module (LEM). The LEM consists of an upper part (ascent stage) that houses the astronauts, and a lower part (decent stage) that holds the braking rocket used to land on the moon. When leaving the moon, the ascent stage blasts off, leaving just the decent stage on the moon. In the film, the entire LEM is shown sitting on the moon, which is impossible since the astronauts came back to earth.
Continuity mistake: Carly's shoes appear to mysteriously alternate several times between black stiletto heels and black ballet flats in-between shots during the climactic action sequence. This is most noticeable during the collapsing building sequence as well as the scene in which Carly speaks to Megatron.
Visible crew/equipment: In the first overhead shot of the Autobots entering Chicago, you can see a small black camera cart in front of Bumblebee and Mirage. (01:47:45)
Continuity mistake: In the first scene with Carly coming up the stairs she is wearing a white cap, when the camera changes to the front view and she is holding the stuffed rabbit the cap is gone. (01:01:30)
Factual error: Many of the Washington, D.C., scenes show skyscrapers in the background, but there aren't any in D.C.
Visible crew/equipment: At the beginning of the parents taking Sam around to interviews. A camera and rig can be seen in the reflection of the driver side door.
Plot hole: When we see Sentinel Prime being extracted from the Ark by Optimus, we can see that Sentinel Prime already looks the same way as he does throughout the rest of the movie. The Ark crash landed in the 1960's, the Rosenbauer Panther Fire Truck didn't exist in the form we see Sentinel Prime transform into. All of the other Autobots came to Earth in their proto forms and adopted a disguise when they arrived [we see them scanning alternate modes - one Decepticon is shown doing likewise in this movie.]. Sentinel Prime already has his disguise when on the ark, which isn't possible.
Continuity mistake: When Sam is first shown at his new flat and the two small robots appear, Sam has a small argument with them, and takes one of the robots in his hand to put him on the floor, but in between these two shots Carly walks in front of the camera thus focusing our attention on her, but if you look at Sam putting the robot down, there is nothing in his hand. And when it's only him in the shot again the robot comes back. They must have missed adding the CGI maybe because he was in the background of the shot at the time.
Factual error: Several references are made to objects being on the dark side of the moon. The moon's rotation is locked into its orbit, meaning the same side of the moon always faces toward Earth. The dark side is simply the side facing away from Earth (which doesn't always make it dark since it receives sunlight when the moon is between Earth and the sun). For plot purposes, the Ark has to have landed on the dark side of the moon or else it would be visible using Earth telescopes because it is so big. But when we see Decepticons hidden on the dark side of the moon crawl out of the dust, Earth is floating in the background, which would be impossible since Earth is not visible from the dark side of the moon.
Revealing mistake: In the scene in the Russian bar, Dutch takes the bartender's gun. When he turns to hit her, the face of the stuntman replacing Alan Tudyk is visible. (01:03:40)
Factual error: After Sam and Seymour visited the Russian cosmonauts, they were attacked on the Interstate by three Decepticons disguised as dark SUVs. During this part of the movie, they are in the Washington DC area. However, during the chase, a green interstate sign is passed by and knocked down that is for I-88 to Aurora. This interstate is in the Chicago area.
Revealing mistake: When Bumblebee says goodbye to Sam, Bumblebee is leaning with his right arm to the construction. When the camera rotates, you can see that his hand is moving through the structure, making it a flaw in the CGI.
Other mistake: In the scene with Richard Nixon speaking to the Apollo astronauts, the TV showing the phone call shows a lamp behind his head, and the seat being right behind him. But if you look at the actor sat there, there is no lamp, and the angle of the camera shows the chair would not be in shot.
Visible crew/equipment: In the flashback scene with Sam and Carly at the White House, the reflector screen is seen in Carly's glasses.
Continuity mistake: When the Dreads knock over the freeway sign, the distance between the two green signs keeps varying.
Continuity mistake: During the chase with the black GMC's, Mirage has black rims in Ferrari mode. When they finish the chase, he now has chrome rims.
Factual error: In the opening scenes of the movie, set in 1961, the Very Large Array in New Mexico is shown. The Very Large Array did not exist in 1961, only being approved as a project by Congress in 1972, and being completed in 1980.
Continuity mistake: When Sam and Dylan are fighting, the clock behind them changes to different times every shot. It starts at 00:40, then 02:25, 00:15 and 11:00 in the following shots.
Revealing mistake: When Megatron is about to destroy Lincolns stone throne, his shadow appears only in the shots where he is visible, but in the shot where only the throne is visible and Megatron is about to destroy it, his shadow is gone.
Answer: Mudflap and Skids (the two idiot robots I believe you are talking about) were removed from the film due to negative fan reaction. While we don't hear what happened to them in the context of the plot, no reason not to assume they were killed in fighting between the movies. Arcee and Chromia (2 of the motocycles) were killed in the last film.