Both are true. The pirate ship being sunk is absolutely a running gag in the Asterix series, and in fact I had a vague recollection that the raft scene also app

Both are true. The pirate ship being sunk is absolutely a running gag in the Asterix series, and in fact I had a vague recollection that the raft scene also appeared more than once, but once I took a closer look, that appeared to be wrong. So, lots of ships of this particular band of pirates being sunk, and once they are posing on this raft in a classical way.