What will happen to my houses and cars on the server because I'm permanently banned and I'm unsure whether I'll re appeal within the next few weeks / months. Do I get refunded when they're taken or do I lose everything?
Nope. Houses get taken away in a month or so (45 days I think) and you can't get them after they are listed on Silver Trading's properties. Your vehicles however are unlikely to be wiped as far as I know.
Properties (houses, businesses) are wiped from a character after 31 days of inactivity and do not get refunded. Any items inside of them (weapons, drugs, ...) are removed and the property is given to Silver Trading and can be bought by another player.
Vehicles do not get wiped.