My friend would like to leave Poland for the Christmas break in December, can he only travel with a decision if he has not received his temporary residence card?

The decision on granting a temporary residence permit legalizes your stay in Poland, but it is not a document entitling you to cross the border. With the decision, you can legally leave Poland straight to your country of permanent residence, there will be no possibility of transit, e.g. from Poland through Germany to the country of permanent residence. The residence card together with the passport entitles you to cross borders.