Rule reminder
Tense sequence with 'a meno che (non)': present/future main clause → present subjunctive (simultaneous/future condition); present/future main clause + completed prior condition → present perfect subjunctive; past main clause (indicative or conditional) → imperfect subjunctive (simultaneous) or pluperfect subjunctive (prior completed action).
Lo incontrerò domani, a meno che non _____ qualcosa di imprevisto.