For me I've actually done it just out of curiosity. My Talonflame has 309 Speed at level 100 before I reset bagged it and it dropped 15+ points. So resetting it doesn't allow it to keep it's Ev's being that it's the only means of you using to EV train. So no it will not it'll be as if you got it to 100 by using only Rare Candies meaning no EVs.
Depending on the level, the Max stats will still be broadly similar to what they would have been anyway. If around level 80, than the difference would be barley noticeable and wouldn't really affect the max damage output / minimum damage received.