With or without religion lives still have to come to an end. Religion plays no part in death rates. If it were we would have 2000 year old Christians or 1500 year old Muslims. No matter your religion you are very lucky if you even make it to the ripe age of 90. Religion may play a role in where you go after death but does not play a role in the death rate.
If there were no religion, the world would not be a safer place. Some religions are peaceful such as Christianity and some are violent such as Islam. But if people were all atheists they would not have any moral compasses and the whole world would look like some third world African nation.
If there were no religion, death rates would definitely increase. People having laws such as the Ten Commandments keeping them in line stops and prevents more murders and suicides than could ever be counted. If people did not have moral guidance of religion, our society would be much more bloody than it is.
Religion gives people a reason to live. It gives people a purpose to life, and should only keep them alive and not dead. Only in sacrificial religions, which are uncommon in Western society, will the death rate increase. Religions should keep people alive because they will want to stay alive as long as they can.
Religion has been one of the big institutions that set people up in opposing camps so that the wars that break out among various followers can be huge. But if religion were not here, we would as ego based human beings set up other institutions that would be just as divisive.
At this point in time we don't have crusades, witch hunts or clan war over religion. As far as I know, the Muslim extremists are the only people killing for religion. And frankly, they don't do all that much. I personally know lots of people who were suicidal, and found an escape threw religion. The point is religion saves lives as well as taking them. And I wouldn't be surprised if it saved more.
Most people feel that they need religion to guide them because it's their instruction manual and personal identification card to help keep them "Enslaved to the System". Without religion we would have even more people feeling the need to "Go to Extremes" just to belong to something no matter what the costs are to themselves or others around them. However I would love to see this world without religion because not everyone will be a lunatic or too incompetent in a world without religion because there are plenty of other tools other then religion that are being used to keep as many people "In Check" as possible . However some people are just too rebellious and evil to be apart of this reasonable "System of Control" and so must have a harsher more strict form of enslavement to ensure both their success and the success of others.