I really don’t think he ever intended any of his apprentices to be long term, he just recruited the strongest force user he could find, and once a stronger one showed up he’d recruit that one. That’s what happened to Dooku when Anakin bested him in battle, then tried to do the same thing when Luke showed up, replace his old apprentice with a newer model

Maul was just a weapon. He wasn't even an official Sith apprentice, as Darth Plagueis was still alive until the night before the Battle of Naboo. Maul was the equivalent of Ventress and Dooku's other Dark Acolytes during the Clone Wars, an underling beneath the two Sith.

As well as being a schemer, Palps was also an opportunist.

His long term plans are only ever about his own survival, the characters within them are merely replaceable moving parts. If a new chance comes along which Palps views as useful, he'd happily ditch anyone.

Probably not

I mean you could say the same about Dooku because he was with him for the entire Clone Wars but I guess eventually Palpatine would have to find a way for Dooku to no longer be his apprentice to allow Anakin to be his

^ Yeah, he did that at the start of Revenge of the Sith.

Even if Maul hadn't 'died' on Naboo Sidious would still have replaced him. Look at what Dooku does, how he presents himself to those he wishes to manipulate, ally to the CIS and so on. Maul couldn't do that his very appearance would frighten most people. Dooku has a story people can relate to they can sympathize with him, a Jedi who left the order because of its corruption etcerta, Maul doesn't have that. So to work the CIS the way he does Sidious replacing Maul with someone like Dooku was absolutely necessary.