Flushing will get rid of any remaining nutrients past or present, it can also break down salt buildup so your root can only bring in what's needed. I don't think I've come across anyone or any reads who don't at least recommend flushing with plain water. There are flushing solutions...but some may work and some may not...not all nutrients and supplements work magic.
But ultimately its up to you, if you decided not to this grow and do on another...definitely document the taste and smell of the buds to compare, then you be the judge.
Mollases is natural and I believe it is safe up to the end from your last few weeks of flowering.