Ok, Joker dies. finito. Gone. ... then what? Seriously?
Batman kills one of his greatest foes, and who steps up to take joker's place, who in turn will get killed? If anyone can ever step up?
Besides, batman has killed, though it hadn't always stuck.
http://www.cracked.com/article_20111_the-6-most-brutal-murders-committed-by-batman.html
There's a certain level of creativity required to make a memorable villain, and once you throw it away, you gotta do something new. If the dead just get revived somehow then what's the point?
Mooks, goons, etc. sure. Especially if they're dangerous and never need to be seen again.
Honestly, Batman nails why you just don't kill. It escalates stuff. You kill, and the rest take notice, and step things up.
Then there's the rivalry mentality. I mean comics have explored joker killing batman, who then went more insane and started being batman.
And to be fair about the gif the OP put up, how do we know the soldiers inside are dead? It's entirely possible, and even desirable that the vehicle be able to take a hit without the inhabitants dying. Better to have to repair a crippled vehicle than repair a person.
Remember the Evil Overlord rules! No body, not dead!