I don't doubt that Messi thought about coming back or at least entertained such thought, however all along I think we were most likely a distant second, if not third option, if things had turned favorable for us (La Liga approves the viability plan, we clear enough room to accommodate him etc.) quick enough instead of possibly dragging through the summer with no end in sight, he probably would have given it a more serious thought.
I'd venture to guess that Miami has been his first option for a while, there is no way he decided to join them last-minute due to us failing to come through etc., they probably had started talking a while ago and reached some sort of agreement for him to join if he chooses so. It all makes more sense, Miami offers something new, much more relaxing (at this stage of his career when he has won everything, he doesn't care about another trophy anymore, family comes first) and less toxic (with all the media talking about him in Barcelona and elsewhere in Spain and his strained relationship with Laporta etc.) compared to returning to Barcelona. He expands his brand and business in the US while his family enjoys nice life.
It was the media, the likes of Gerard Romero creating and instilling this sense of false narrative and hope that there was a great likelihood that he would return. More like their wishful thinking got in the way of rational reporting.