What if Botox is mistakenly mixed with a reconstitution solution that is only benzyl alcohol and has no sodium chloride?

I encourage you to contact the manufacturer of Botox directly as this occurrence is not typical. The Botox may remain inactive when not reconstituted properly.

Most likely the effect of the botox will be attenuated as the protein is not in its active state, it may even be denatured by high concentrations of alcohol.
As no clinical studies have been done it will be difficult to give a definite answer to this question.

The only one who may answer this question accurately is calling Allergan (Botox parent company). While searching the side effects of Benzyl alcohol online, it does not seem to be harmful and is used as a preservative in many medications. The most common issues were redness at the site of injection. As far as the ph and if it inactivates Botox, I am unsure.