This is a bit of a head-scratcher. My instinct was to say 'of course, all variable are retentive'.
But more careful consideration says that maybe they aren't.
Variables in CCW have an access right attribute: they can be Read/Write, Read Only, or Write Only. Frankly, I'm not sure how these access rights apply to logic or HMI channels. I know I can't write a value to a Read-only variable with ladder logic.
Variables also have an Initial Value, which is applied to them 'when the virtual machine starts the execution of the resource'. That sounds like a fancy way of saying 'when the controller goes into RUN mode'.
The Help file says this can be the default value (usually zero), a value given in the the definition, or a value of the 'Retain' variable when the virtual machine is stopped. Again, that sounds like a fancy way to say powered down.
The Micro 810 controllers have a Retained field in the variable view. Micro 830 controllers don't.
I know for sure that I have timers and such that have the .PT value set via a ladder 1_Gain instruction when user presses a button. Those are Read/Write variables and those survive a power cycle.
So this post is one long "I don't know".