Why did Rufus Scrimgeour not make efforts to remove Dementors from Azkaban as soon as he took over from Fudge?

Question

By the time Scrimgeour took over as Minister, the Dementors had long-since changed their allegiance to Voldemort. During the events of Book 5, we see a large scale break-out of Death Eaters from Azkaban, aided by the Dementors.

Although the Ministry didn't acknowledge this change of allegiance in Book 5, they eventually did by the end of the book. Following the battle at the Ministry, Lucius Malfoy and other Death Eaters were imprisoned and sent to Azkaban, which was guarded by the Dementors (known allies of Voldemort at this point) again.

....said Fudge, looking tired and flustered as he addressed reporters. "It is with almost equal regret that we report the mass revolt of the dementors of Azkaban, who have shown themselves averse to continuing in the Ministry's employ. We believe the dementors are currently taking direction from Lord-- Thingy.

....

'The dementors have left Azkaban,' said Malfoy quietly. 'Dad and the others'll be out in no time ...'

'Yeah, I expect they will,' said Harry. 'Still, at least everyone knows what scumbags they are now--'

Both quotes are from OotP, Chapter-38, The Second War Begins

My question is, why did neither Fudge (post the revelation) or Scrimgeour after taking over as Minister of Magic, not bother changing the guards for the imprisoned Death Eaters? Why would the Ministry risk imprisoning them at a place which was guarded by Voldemort's known allies, especially since the rest of the wizarding world was also aware of this information at that point? (Considering the Ministry was always trying to save face with the general wizarding population)

I get that Fudge who was already a sloppy, non-proactive leader, was probably in pieces and hit rock-bottom post the sensational Voldemort revelation. But wouldn't Scrimgeour, (who seems a lot more sensible, and was someone who didn't take Voldemort lightly, acc to Dumbledore) have most definitely acted on this?

Answer 1

The Dementors had definitely left Azkaban.

Fudge confirms as much at the start of Half-Blood Prince.

"I thought the Dementors guard the prisoners in Azkaban?" he said cautiously.
"They did," said Fudge wearily. "But not any more. They've deserted the prison and joined He Who Must Not Be Named. I won't pretend that wasn't a blow."
_{(Half-Blood Prince, Chapter 1, The Other Minister).}

So Scrimgeour didn't choose to keep the Dementors on (which would've been a very misguided decision). They had already left of their own volition. Scrimgeour presumably had other people guarding Azkaban, although to my knowledge we're never told who these people were or what precise arrangements were put in place.

So what about Malfoy's quote?

"The Dementors have left Azkaban," said Malfoy quietly. "Dad and the others'll be out in no time..."
_{(Order of the Phoenix, Chapter 38, The Second War Begins).}

I suspect that Malfoy means that breaking out of Azkaban is no longer the impossible feat it once was. With the Dementors gone, dangerous witches and wizards who'd been living in a constant state of depression and insanity for years upon end would've been fully restored to their old selves again.

"...when they let me out, it was like bein' born again, ev'rythin' came floodin' back, it was the bes' feelin' in the world."
_{(Prisoner of Azkaban, Chapter 11, The Firebolt).}

Additionally, Voldemort and his followers had already been restored to their old prominence by this stage. It wasn't a motley crew of misfits trying to escape but an organised criminal resistance trying to break in. This security threat was significantly more challenging to counter than anything the Dementors had ever faced beforehand.

To make matters worse, the people or creatures tasked with guarding Azkaban were untested and untrained. They had taken over the running of Azkaban at very short notice and with no prior warning. It's quite likely that they would've been quite disorganised and hapless, especially in the early stages. This made a mass break-out at Azkaban quite likely.

So, yes, Draco did have sound reasons for thinking that Lucius may have been able to escape Azkaban relatively quickly. But this was because of chaos in the management of the prison rather than because the Dementors were still there.

Answer 2

When Scrimgeour became Minister, the Dementors had already left Azkaban.

Fudge tells the Muggle Prime Minister that the Dementors have deserted their positions at Azkaban and gone to join the Dark Lord. He specifically states that they're no longer guarding Azkaban.

“And as if all that wasn’t enough,’ said Fudge, barely listening to the Prime Minister, ‘we’ve got Dementors swarming all over the place, attacking people left right and centre …’

Once upon a happier time this sentence would have been unintelligible to the Prime Minister, but he was wiser now. ‘I thought Dementors guard the prisoners in Azkaban?’ he said cautiously.

‘They did,’ said Fudge wearily. ‘But not any more. They’ve deserted the prison and joined He Who Must Not Be Named. I won’t pretend that wasn’t a blow.” _{^{- Harry Potter and the Half-Blood Prince, Chapter 1 (The Other Minister)}}

Fudge tells the Muggle Prime Minister this when he goes to update him on the return of the Dark Lord and related events in the wizarding world, as well as introduce him to Rufus Scrimgeour, his newly appointed successor. Fudge had only been fired three days before this meeting, so Scrimgeour couldn't have been Minister for any more than three days.

“My dear Prime Minister, you can’t honestly think I’m still Minister for Magic after all this? I was sacked three days ago! The whole wizarding community has been screaming for my resignation for a fortnight.” _{^{- Harry Potter and the Half-Blood Prince, Chapter 1 (The Other Minister)}}

Therefore, Scrimgeour wouldn't have needed to do anything about the Dementors, since they were no longer there and had already left before he became Minister.