While it is quite possible for our KINO (Heavy Duty) fabric to survive outdoor, it’s not something we would recommend over a long period of time actually. Ideally, the fabric should be UV proof and water resistant, but even the IKEA couches themselves aren’t made for outdoor conditions. What it’s lacking is a self-drying design whereby the water would be able to easily drip off the furniture, and partly also for its frame to be able to breath.
That's why you’ll find many outdoor furniture using rattan, plastic and coated with rust&weather proof coating.
TLDR; Basically the cover might survive, but your sofa will have mildew and its frame rotting after a year (even with water proof cover).
Having said that, we'll definitely look into getting an outdoor fabric range so keep an eye out :)