"Is it ok for a slave to ever withdraw consent?"...anon.
Yes i think so.
However withdrawing consent is not something to be taken lightly, such as being used as a 'get-out' because one doesnt want to submit to something, but i guess perhaps it depends on whats acceptable within an individual relationship.
For me to withdraw consent it would have to be for very good reasons..such as
my Master not being in a fit state of mind (perhaps due to illness, alcohol) to make sound judgements.
my responsibilities to my childrens welfare threatened in any way ....i may be his slave but im a mum and for as long as they are dependent on me in the respect of them living at home....they come first...so something like hitting me in front of the children and/or exposing them to things they shouldnt be.....children need a safe/secure/loving environment.
* just to add in respect of above, i dont mean accidental incidents such as kids walking in when your having sex, or finding an implement etc....heck these can happen*
disregarding my emotional and physical welfare (outside of a 'scene') ie constantly or an example could be him having unprotected sex with various people or expecting me to
Its really about SSC (safe, sane and consensual) or RACK (risk aware consensual kink..although perhaps this pertains more to bdsm activity than the relationship as a whole) but either fit, yes we both like a drink, if he has been drinking we dont 'play' well not in anyway that involves bondage or anything 'extreme' and its certainly not the time to be having serious discussions when alcohol is involved.
I trust him not to behave in any of the above reasons i gave, he has not given me any reason not to trust him...but they are examples of circumstances that would make me withdraw consent and would have a huge impact on our relationship.
So, slaves (how you define that is up to you) contrary to myth or fantasy can leave, withdraw consent if circumstances call for it...anyway thats my thoughts.
*edited to add that i dont think withdrawing consent necessarily means the end of a relationship*