Palpatine's Carefully Orchestrated Plans
Anakin Skywalker's reckless behavior almost destroyed all of Palpatine's carefully orchestrated Clone Wars plans - and nearly changed the course of the entire Star Wars saga. Palpatine is an exceptionally ruthless and cunning character, and he envisioned the Clone Wars as the ultimate Jedi trap. Everything was carefully orchestrated; there was not a single battle he ignored.
Star Wars Hints At The Origin Of Palpatine's Clone Wars Plan
Part of it, of course, was that Palpatine wanted the Clone Wars to break Anakin Skywalker's resistance to the dark side. But, as flawed as Anakin may have been, he was still a hero of the Clone Wars - meaning the Chosen One was often working against Palpatine's agenda. In fact, there was one moment when Palpatine's plans were profoundly threatened by Anakin Skywalker, and when he feared his potential apprentice would die.
Palpatine Feared Anakin Skywalker Would Die Due To His Recklessness
In Star Wars: The Clone Wars season 1, episode 2, Anakin Skywalker and Ahsoka Tano ignored orders to go on a rescue mission for Jedi Master Plo Koon. His ship has been attacked by a secret Separatist superweapon, the Malevolence, and he was stranded in the Abregado system. Palpatine's plans for the Chosen One suddenly conflict his other strategies, because he wanted the existence of the Malevolence to remain secret.
Anakin Skywalker and Ahsoka Tano in Star Wars The Clone Wars season 1, episode 19 Storm Over Ryloth
Palpatine is visibly frustrated when he learns Anakin is in the Abregado system. To make matters worse, because this mission was not authorized, Palpatine knows that Anakin doesn't have backup. He is going into a dangerous situation with no support. Further, if he and Ahsoka were to discover the true intention of the Malevolence - and who was behind it - Palpatine's carefully crafted web of manipulation over Anakin could unravel.
Anakin's Death Would Have Ruined His Plans
The Clone Wars were carefully engineered in part to break Anakin. Palpatine needed him alive, and Anakin's decision to go off on his own without authorization risked everything. As seen in Star Wars: The Clone Wars - especially in the episodes featuring the Mortis gods - Anakin's connection to the Force was unparalleled. That made him the perfect candidate for a Sith apprentice, and Palpatine had been grooming him for years. If Anakin were to have died because of this mission, Palpatine would have been left without a suitable replacement.
While it is possible that Palpatine could have found another young, moldable Jedi he could corrupt, they wouldn't have been as good a candidate as Anakin Skywalker. Because of his past experiences, Anakin carried around a lot of hatred and anger. That combined with the fact that the Jedi told him from the very beginning that he was both special and someone to be feared made a perfect recipe for corruption. His miraculous birth via midi-chlorians meant that he contained unusual power. All of this made him the best candidate, and no other Jedi would have fit the bill so exactly. Palpatine's main Star Wars plans would have been massively disrupted.