I also agree, depression is very tough, and after reaching a low point like that once, (like just about everyone does), I agreed never to let myself get there again.
But it depends on person to person, alot of my close friends know that I lost another close friend, kinda like a sister, who took her life last week (though not a teenager), she was overcome with grief (reasons will not be explained as it isn't a pity contest), and saw it as the only option. When I found out those reasons I could understand how alone and hurt that person felt, but it still just seemed like the wrong way to find a solution to those said problems. If a person believes that they "make it to a better place", and they (lets say hypothetically), look down on us, would they actually feel much better seeing the grief around them, anger, and confusion caused when people do this?
In this particular case, it was pretty much impossible to detect until the very last days that this person had so much grief, because they carried themselves so happily and put others first so much that it didn't seem like them.