Does anyone really know? Its uncharted territory. I think its literally impossible to answer the question without your own biases and expectations getting in the way. There are too many variables, too many decisions that have yet to be taken, decisions relating to questions that havent even been asked yet. So we are all basically arguing according to our own expectations about what we think will happen.
I think the only thing that comes close to being a fact is that in the short term, economically, it is going to be a shitstorm. Hard Brexit that is. Exactly how much of a shitstorm, how fiercely the shit will lash down, and how long for, I dont think anyone really knows and I dont take any model that predicts it particularly seriously, but I think the storm will come.
Long term I think we are all speculating. Not that I dont have conviction that my own views on it are right. I do fancy I have a pretty clear idea of what will happen. But I cant back those views up with facts or argue them objectively, or know with any degree of certainty what it means for English people living in England. None of us can. How can we know what deals we will make with China or the US? What regulatory concessions we will make in order to facilitate those deals. How much financial services business will move out of London. Could be none, could be a hell of a lot. In the long term, either, or anything between, is all possible, and will all have massive implications for growth, and thereby for the economy, and living standards of English people in England.
Also with immigration: how many immigrants will we let in? What kinds? Will any people be deported - people found to be here illegally, people claiming to be refugees but found by the government of the day not to qualify? In the long term, will England ever start to feel "English" the way nostalgic Brexit voters wished it did again? Or will it merely stop changing as quickly as it has in the past decade or so? Or will it carry on as much as ever, as we restrict Europeans and invite more of our commonwealth and Chinese brothers and sisters? That cant be ruled out as part of any bilateral trade deal we do with any of these emerging markets.
Anyone who answers the question above is only speculating, nobody can give you a simple answer. If they do, you should recognise it for what it is: a guess. Then you have to work out for yourself whether it appears to be an educated guess or not, how many of these variables the person making the guess has considered and what kind of position they are in to predict the answers to them.