Can a vegetarian roast ever look and taste like beef?

Probably, but who cares?  You don't go vegan for the taste.

It would never taste the same to see and eat.

I don't bother to eat things that are pretending or trying to be other things.

Just like I don't do diet sodas, low fat snacks, fake bacon, margarine, sugar substitutes, etc.  I like to eat real, healthy food and indulge when it's appropriate.

I saw some of that vegetable stuff that looks like raw ground meat and it was terrifying.  It really did look like hamburger (which I might cook for my dogs but don't eat myself).  They are doing whatever it takes to make something look like meat which means they are NOT paying attention to making it healthy and balanced.

Real food has nutrients in useful and not entirely understood relationships.  By real food I mean an apple. A sweet potato.  A bunch of chard.  A piece of good quality beef or chicken.  A stick of butter.  A carton of milk.  The less that is done to food the better, and if things need to be done to it do it yourself so you understand what has been done to the food before you consumed it.  

A plastic package of stuff that looks like raw ground beef but isn't even a meat product?  SHUDDER.  I can't even imagine what it would take to make that happen.

The difference would be negligible. The only thing is that if you choose to eat vegetarian meat, it more than likely is higher, much higher than regular meat in sodium.

It may be possible to make one to look like beef, but I dont think it will taste like it.

Not on your life.

Maybe you should have a read of one of the 'Bish Bash Bosh' recipe books.  The Authors have tried to replicate the taste of Bacon, by using various pastes made up of vinegars, herbs and spices. I'm sure that you could replicate a beef like taste and texture, perhaps using some fungi or fermented veggies etc...

that would seem to contradict the purpose of being vegan. 

You seriously believe there's no roadkill in your veggie salads?

They taste better if done right.