Depending on how high tech your setting is, someone or something is going to be keeping an eye on those camera feeds. A low security facility might have your classic "guard reading a magazine when he should be watching the cameras", but better than that should have someone keeping an eye on the screens at least 80% of the time barring distractions. Higher sec facilities would have multiple people watching the feeds.
Higher tech settings would have more ways of compensating for the above (hacked camera feeds displaying looped video) but they'd also have more ways of catching it (AI assistant to monitor for unusual data coming from cameras, intruder detection algorithms to draw guards attention to movement on cameras, etc).>remove guards
A even a low security facility would have guards checking in on a set schedule to identify when guards go missing. Higher sec facilities would check in even more often. Depending on how alert the facility is (and how strict their security is), a guard going missing can give the party anywhere from a 5 to 30 minute window for the party to cause havoc before the guard is noticed as not having checked in (and then a period of time before they decide it's suspicious and investigate or go on lockdown). Additionally, if things get too rough the facility will probably have outside assistance they can call in on. Low sec facilities might call the police, higher sec facilities would probably phone in a private strike team or the military.
Depending on the tech and security level, guards may have GPS trackers to monitor their movements. Guard stop moving for a long period of time when they should be patrolling? Better go check on them. A really fancy one might have life monitors to alert when something goes wrong (no heartbeat would be a major one, but also things like greatly accelerated heartbeats as well).>loot EVERYTHING
Pretty much everything important should be tagged for easy tracing later.