Substep ruling help

I'm trying to build a blue green white edh blink deck including some of the new eldrazi etc. I'm trying to determine if prized unicorn is a worthy addition. My commander is Roon of the Hidden Realm. If I declare unicorn as an attacker alongside others, my opponent declares all blockers against unicorn, and I then blink unicorn with Roon what happens to the blockers? Are they re-declared since the target no longer technically exists or are they just wasted? In essence, can I force my opponent to repeatedly block nothing but air and keep my precious unicorn alive while swinging through for massive face? I've never really encountered this scenario before

Yes you can. Once the blockers are declared there is no way for the opponent to reassign them. So you'll get to swing for mass amounts to the face each turn.