Well dad you know I don't no fan of these serpent pens but I do admire what you do and the causes you do it for init?
I do notice you are using polyprop, you also know that I worked for years with loctite to find a glue that would stick polyprop with limited success.
CA is not a glue that holds for long, polyprop is susceptible to expansion and contraction with temperature changes and will give to break the joint in time.
How long is a piece of string for the answer as to when but they will fail, sorry to be a party pooper but they ain't a pen I would want in my pocket.
Much better to use dyed woods rather than plastic and wood due to the differing expansion rates of the materials.
Unless they are show pieces kept in a stable environment and not handled often.