There is few things way I see it
- mortgage , where you need financing and there you may want to talk to bank whenever they be fine when you move abroad
- legal (loss of permit) - that should not be an issue to keep the hause as there is many houses owned by people that have no swiss permit in places like Davos, Gstaad etc.

should you have withdrawn pension plan for purchase - I am not entirely sure you'd need to return it . Certainly you would not be allowed to sell house without return of the found - while it may depend to where you departed after moving from CH I guess.

Income-tax from rental should be in country of your current residence ( that would be the case for anyone living in CH and renting his house out in Spain as example). Real-estate taxed however needs to be paid in country where the real-estate is located .

I am not aware of what these taxes would be in CH to be honest ..

This is incorrect - rental income is (usually) taxed in the location where it is earned. Swiss tax is impacted through the total income band/rate but the actual rental income is not taxed here.

When we bought in CH in 2005 we were told that I cannot rent out our house with a B Permit, as a non-EU national, and would have to move the property and mortgage to my husband's name.

Fast forward to 2019, C Permits then Swiss Passports. I informed the bank of our intention to rent out our property and they confirmed with no issue at all. We expected to have to pay back our Pillar 3s that were pledged and pension withdrawal but no.

They requested our new address to which I said Australia temporarily for a year and alarm bells starting ringing. Letter sent that mortgage was to be due in 1 month in full. Yeah - we'll just have a whip 'round

Seems we need to be resident in CH. No where did it say that in the mortgage agreement but that's the bank's policy. They were happy to fix the mortgage for 5 years, earn some more interest and the banker got that sale for his bonus. We need to be back in CH to renew the mortgage or find a new bank or pay it back then.

yes, you are right

reference : https://www.braunlaw.ch/fachartikel/...rische-steuern

for that reason alone it's convenient to use Treuhänder and best one you can find ...is to ask Tax office for one - as they know each other for years and often these are guys that once worked for tax office