In the most literal of senses, I don't sense that there is much of a choice.  Ishiguro establishes the donor condition in the novel as one in which accepting one's fate is to face destruction in the form of being "completed."  What has become clear out of the Morningdale Scandal discussion of chapter 22 is that the conditions for clones have become worse since the childhood times of Ruth, Kathy, and Tommy.  Things have become worse for this contingent so that one has not choice but to face destruction in the acceptance of their fate.  Their fate is one of "completion."  There is no avoidance of this.  Hence, it does not seem like there are two choices, at all.  This is the central concern that lies at the base of Tommy's outburst in Chapter 22, as he feels that Miss Lucy was right in that the clone children should have been made aware of their destiny.  In the final analysis though, there is little choice that the clone children have because the configuration of society has done enough to place them "back in the shadows."  Through their marginalization, their fate has become destruction so there really is no choice available to them.  Destruction has become the underlying element no matter what.  The characters in the novel become aware of this in a painful manner in that each one becomes "completed." I think that this demonstrates that the reality of acceptance of their condition as one of personal negation and destruction becomes inevitable.  There is little choice in the matter.