Alcohol can postpone the inevitable in withdrawal. There are also medical solutions such as a benzo taper that makes withdrawal relatively painless...but they should be done in an inpatient situation, IMHO.
The alcohol in the Nyquil may have lengthened your taper, but doubtful that it's going to come back with a vengeance.
BUT!!!
Withdrawals are highly unpredictable. It's good to have a doctor available (or urgent care or the ER) just in case things take an unexpected turn, no matter how unlikely.
Good luck on your detox. How are you planning to stay sober once you get there?