I disagree that it's the dom's choice. If people aren't willing to play then play is not consensual. If a sub says she is too tired then that is what it is. If a dom doesn't think that being tired, or being sore, or sick, or having a headache, or anything else are good reasons to not play then the dom has options ranging from expressing displeasure through ending the relationship to find a more satisfying one. What the dom does not have a right to do is to force himself on an unwilling partner.

(of course there are some relationships in which consent has been negotiated ahead of time and in which both people are explicitly comfortable with the dominant making these kinds of decisions without in-the-moment consent from a sub, but if you haven't explicitly talked about that then you're treading on very dangerous ground).