Warning: the following contains SPOILERS for Ozark season 4, part 1.
Ozark season 4 part 2 will be the first time for the Navarro cartel to operate without the cunning Omar Navarro (Felix Solis) holding the reins, but even though this makes the cartel more vulnerable, FBI agent Maya Miller (Jessica Frances Dukes) still missed the bigger picture when she arrested Omar. While Omar gets familiar with the inside of a jail cell, the fate of the Navarro cartel is left in the hands of Omar's dangerous and erratic nephew Javi Elizondro (Alfonso Herrera). This is all because of Maya's decision to defy her superiors' orders and arrest Omar.
In Ozark season 4 part 1, episode 7, “Sanctified,” Marty (Jason Bateman) and Wendy Byrde (Laura Linney) finally convince their boss Omar to strike a deal with the FBI. As part of the deal, Omar cedes control of the Navarro cartel to Javi. The initial arrangement is for Omar to spend time in prison and provide the FBI with enough evidence to arrest Javi and other cartel leaders – in exchange for immunity. At the last minute, FBI agent Clay (Tess Malis Kincaid) changes the terms of the deal, forcing Omar to reclaim his role as the Navarro cartel kingpin while paying taxes and working as an informant for the FBI for the next five years. However, things then take a more complicated turn for the upcoming final act of Ozark because as Omar is about to climb on his private jet and return to Mexico, Maya and several other law enforcers move in to arrest him.
Ozark's big season 4 twist puts everyone in a tighter spot. Following the arrest of the calm and calculating Omar, who is responsible for the rise of the Navarro cartel, the FBI is now forced to work with the unpredictable Javi, who is more of an enforcer than a drug kingpin. While Maya is correct about how Clay and her superiors made a deal with Omar for the financial benefits it affords the FBI, Maya's bosses are also right about Omar being more valuable as a fairly reasonable and controllable informant – as evidenced by the thousands of dollars worth of drug seizures that Omar has already handed to the bureau. Instead, Omar gets replaced by Javi as the villain in Ozark season 4, and he is a much less valuable asset to the FBI. In short, although the FBI stands to make some money from striking a deal with Omar, it would've also allowed the bureau to develop a more effective long-term strategy for dealing not just with the Navarro cartel, but the entire Mexican heroin industry.
Moreover, by unexpectedly arresting Omar, Maya also put the Byrdes at risk, as the arrest makes it appear as though the Byrdes betrayed Omar. Even from inside a jail cell, it's clear that Omar still has the power to order assassinations. If it wasn't for Marty and Wendy's quick response to the situation, Maya's decision would've immediately led to the death of the Byrde family during the ending of Ozark season 4 part 1.
Ozark, through Maya arresting Omar, sets up a final confrontation between the Byrdes and Javi in Ozark season 4 part 2. To be fair, Maya's decision also led to instability for the Navarro cartel, as Javi's erratic nature puts the cartel in a vulnerable position. That being said, with Omar out of the picture, this could also empower the Navarros' rival cartels to step up, which only introduces more complications to the ongoing drug war.