Ok,
Since there was no Johnson mentioned, let's assume they planned this themselves, and used a little common sense and gathered the supplies needed well in advance. (this case let's say: sniper rifles, magic support, get away vehicle, replacement vehicle, safe house with change of clothing/sins and yet an other vehicle...)
Right after the shot and death of Knight, expect a combing of the area that the shot came from with in 5 minutes by security. If the runners avoid them, they got a head start.... But that's it.
Within 30 minutes. Corp hackers are combing through every and all cameras starting at the location of the shot and working outwards. They KNOW this was a professional job, so they will be expecting altered data, and may even try to use the trail of false data as a lead.....
While the hackers are at work, fire watch teams are mobilized and sent into a holding pattern in and around the city. Special Ops goes into overdrive looking into every single person in the world with the resources and grudge against Knight. (that's going to be a long list!!)
Knight Errant goes into overdrive (assuming they hold the city contract) within 60 minutes of knight's death and seals off a 12 block radius around the shot location. They also establish check points at every choke point in the city (contract be damned!) expect lockdowned bus/rail/air stations. KE starts pulling in all the usual suspects for "questioning", anyone with even a finger in the shadows can expect to be paid a visit... And not politely. Magical analysis is conducted at shot location. ANY material left WILL be used for ritural casting. (they DID get away... Without injury, or leaving DNA behind... Right?)
Within 12 hours, military intelligence and anti terrorism units arrive in city and begin investigations. Any leads or suspected leads will be followed up aggressively!!
On the corporate level, power will transfer as according to protocols, and will begin to shore up their assets to prevent hostile maneuvers from rival corps. All executives will probably be screened to see if they had a hand in the assassination. Letters and statements will go out addressing the incident with enough spin attached to put the company in the best public image. A reward (probably in the tens of millions) is posted for the arrest or capture of the guilty parties.
If the runners can remain hidden without tipping off Ares, Knight Errant, the military, or the government for 14 days, they are closer to being out if the woods... If they keep their mouths shut about their role in the assassination for the next 10 years, they live. The moment they open their mouths and brag about the job to ANYONE in the shadows.... They die.
No Corp would let the assassination of their head man go unpunished. It wouldn't matter how long it took, they would pursue the assassins forever! It would be like the USA ignoring a killer of the prez. It just wouldn't happen there is too much honor at stake. The Corp MAY however concoct fake evidence to frame someone else for the crime if the rewards where big enough.... But that just means any retribution would come in the night... And if the runners were extremely lucky, be short, bloody and over quick. If unlucky, they would be taken to a corp facility and 'volunteered' for clinical trials for all sorts of projects 'in the advancement of knowledge for mankind'