With the successful killing of Song Maoxun, the Song Clan was truly done for. While there might be other remnants of the clan at large out there, the last bit of the clan's foundation had essentially been uprooted.
The remaining members of the clan were hardly considered a threat by that point.
Furthermore, those who managed to run would probably need to live their days in fear from then on out, like a dog who'd lost its master, and there was also the fact that they were being hunted by the Special Task Force to deal with.
Any other force would probably get rid of them on sight as soon as they were found, especially the other clans comprising the Holy Dragon Corporation. All of them would probably eliminate any remnants of the Song Clan without any hesitation.
They were out to gobble up the wealth of the Song Clan whole, and those remnants of the Song Clan posed a huge obstacle to doing so.