Does 的话 in 这句常挂在嘴边上的话，便点点头答应了 create "If~" subclause?
No, it's not a if...then... structure here. 

话 here is used as its literal meaning， words or sentence.

The main clause is actually 他想起了话. And the 话 he recalled was “在社会上混，什么都得尝试尝试”, which always hangs  on his mouth(implying he often says that sentence.)


  他想起了，&lt;“在社会上混，什么都得尝试尝试”> {这句常挂在嘴边上的}话


So when that sentence came into his mind, 便点点头答应了 he nodded and agree to do it.