Things like this have been known to happen. Sometimes you can find the end filled with around 20 dragons. But a dragon in the overworld is not too bad since I don't think they have block destruction enabled, I could be wrong but I do not think that they do. Sure people might get killed by it but there will always be someone there who can kill it if needed.
That happened to me a while back, I was at someone's base and there were three dragons there. Block destruction is off so its just flying around. The bedrock portal still spawns though, which is rather annoying when it falls in your back woods.
