I feel very strongly about this - and I hope my experiences can be of help to you.....
My partner was diagnosed with Crohn's disease Jan 2016 - but had good health for all of that year apart from us suspecting he had memory issues. An appt was made regarding this but was some months away when last Christmas his physical health took a major downturn.
He was admitted to hospital on 29th Dec and did not come home until 5th Feb - and when I got him home he was a different person.
The hospital tried for 3 weeks to cure him, without success, and it was a dying man they took to surgery for a colonoscopy. We were told he would have a 'bag', and that was the end of that. They knew he had memory problems, but did not tell us that this major illness could affect that.
Six hours anesthetic on top of weeks of fever and ill health, and BANG! Not only did he come home with a bag, he came home with major symptoms of mixed dementia which has now been diagnosed. Our lives have been devastated.
Why? Well, no one explains what a pain it is trying to manage a bag with someone who has dementia. it seems it can be reasonable if the bag has been in place for years before the dementia strikes, but as two 'new' issues life takes on a nightmare quality.
My partner never learnt to manage the bag - he was discharged from hospital and the first night we ended up with the contents of the bag all over him, all over the sitting room, all over the bathroom, the bed - you name it and s**t was there! At almost midnight we had 2 district nurses here trying to sort us out.
Almost a year later - the bag won't stick no matter what we do - the dementia causes him to scratch at it ( common, it seems) and our lives revolve around this bloody bag. The quality of his life is so reduced, and his anguish is palpable. He now spends all day just sat in front of the TV with little interest in anything. We talk about levels of 'fed up ness' and it is usually over 100%.
So, I am aware that surgeons etc do not really ' know' their patients, and often do not explain things fully, because they have no way of knowing whether we will understand the complexities of what they are explaining - that is totally understandable. BUT you need to ask the surgeon/consultant whoever, what the effect of this very major operation will or could be on his dementia - and then start to weigh things up. My partner has been in hospital 4 times this year since the operation - mostly connected with issues from the'bag' - but each time he becomes unwell, feverish, etc the dementia gets worse - vascular dementia especially, does that.
So, my advise to you ..... is be aware there are implications to this operation in respect of the dementia, that having a bag is not simple and straight forward, it can be a total utter nightmare to manage, especially with someone with dementia. You need to speak to the team of stoma care nurses at the hospital. You need to see if you an have carers coming in to deal with the bag for you - we have managed this after almost a year. Because love my partner as I do, I find the stoma itself a revolting thing to deal with. You have this person you love and respect, you try to change the bag for them and there is s**t shooting out of the thing as you do it!! Not pleasant. If I can be of any further help, please pm me.......