So, this proposed alternative ending is terrible for two entirely separate reasons:
1. It shows total ignorance of the mythic source material. Harry has to choose to die, or else the prominent Christian arc of the story fails (I suppose it's little noticed that his parents' gravestone has an apposite Biblical quotation on it that's in line with the metaphysics of dead people in the series). Harry has the comfort of those who have died surrounding him, and his sacrifice is still terrifying, because he doesn't know if he will come back: this is why it's a sacrifice. He has to die. (This is also why he has a stable wife, kids, and friends at the end: dude has suffered enough. People seem to hate this for not being realistic enough in a story about magic.) To kill Voldemort and emerge unscathed is perhaps more 'badass,' but it makes him less recognizably human.
2. The ending is also needlessly cruel in what seems to be the modern style: people really want Don Draper to commit suicide at the end of Mad Men, people debated whether it'd be cooler for Walter White to die or take out a bunch of the bad guys, Boardwalk Empire only rises to any aesthetic heights when devising new ways to show people being killed. An ending can only be 'real' if it's tragic, if it kicks the main characters in the most ingenious of ways. I would think one need only point out that adult life isn't like that, but I'm not sure that would convince anyone.