The biggest mistake this statement makes is in invoking extremes. It’s impossible to surrender and dissolve “totally and completely” until there’s “nothing left of you.” That’s just not how spirituality works.
This is one of those things that stands at the juncture of Eastern and Western spirituality. A person surrenders until they become enlightened, but being enlightened is not the same thing as being God. As you lose individual aspects, you acquire more spiritual ones, and spiritual aspects slowly become heavenly ones.
This happens throughout the course of your life as you learn and grow. At no point is the journey ever done. You die and are reborn, in this world or a different one.
Buddhist tradition holds that your last few lifetimes before ultimate samadhi are conducted in heavenly realms. You’re already not human anymore, since a human form is required, but rather a heavenly being. Yet you are still not fully and completely dissolved, this would mean a total loss of individuality.
Ultimately this is a contradiction in logic. It is certainly possible to experience a feeling of dissolution. These feelings are temporary mental states that cannot continue of their own accord. The reason why is biology, our brains only have so much capacity to bliss out. If you fire off endorphins all the time, you won’t really experience that as bliss, but rather as just normal.
Being human means retaining a slight bit of agency. The spiritual process involves going through occasional periods of Void where agency is muted almost to non-existence, but these things are limited by our evolved mental defenses. Your lack of agency won’t override biological impulses to eat and not jump in front of traffic.
It’s one of those things that sounds neat and awesome, but falls apart into contradiction once you start really exploring the space. The teacher can then get even more silly and try to claim that you don’t really know this stuff after all, but if you ask reasonable and pointed questions, the kinds of wannabe gurus who say this stuff won’t be able to give satisfactory answers. And they’ll beg for your Patreon donations so they can finally quit the job they hate so they can peddle more contradictory pap.
Keep looking, let your feelings guide you, and you’ll find true insight.