Starting form the pit lane was a major disadvantage for the exact reason he went off, really cold brakes on a quite cold day. Brakes are smaller this year so when they are cold they have even less performance then previous years.
When push came to shove Rossberg couldn't do what was needed to be done ( pass Vergne). even with the safety car he should have won, he didn't get the job done no one else.
2nd safety car ruined ricciardo's plan, but when push came to shove he got the job done.
He went off because he made a mistake not because his brakes were cool. He should know, his team should know, that his brakes were cold. Magnussen didn't go off with cold brakes.
And the advantage was a car that could run with a brand new setup to take advantage of the shifting weather.