Hotpoint RFA90

Hello White Goods gurus!!

I have a 4 year old Hotpoint fridge freezer which has gradually failed over the last month. First the bottom freezer compartment stopped freezing and then all freezer defrosted leaving fridge as only functional part of appliance. Last week fridge stopped cooling too. Turned the lot off, fully defrosted for 24 hrs but still doesn’t work. I have called out a Hotpoint engineer who is coming in a couple of days but just want some indication as to whether it is likely to be fixable. Does it sound like a thermostat or gassing problem to any of you experts???? Hotpoint do free parts under 5 years old so should be about an £80 charge only to fix it if it is fixable.