I think they should keep them. I think that the more forms of warnings there are the better. There are a lot of people who live on farms in that area. If someone is outside working, a siren may be their best chance of getting the notification. Also, every form of notification is subject to failure. A few years ago there was a tornado that struck near our house and the weather radio transmitter was not working. The sirens woke me up and we went to our safe place. That was the only warning we had, even though we should have had others. Our house was not hit, but we were only a few miles away and that is too close for comfort.
Phone and radio batteries die, and power goes out in houses. The danger is too great not to have multiple ways of getting warnings. We have all been trained to recognize the sound of a tornado siren our whole lives, and we instinctively react to that. Sure, we may not always hear it, but we also sleep through our alarms, ignore the continual barrage of phone notifications with which we live and turn off our TV when we go to bed. Also, text messages can be delayed by a lot of time when they are sent out en masse. I have gotten some the next day, long after they were sent. Some people never watch the news and don't know anything may be coming, so they don't charge batteries or do anything else to prepare.
During the storms a few weeks ago, I got texts from multiple sources, had the emergency alarm go off on my phone, had calls from the EMA AND heard sirens. I had the best chance of surviving if I had been in the path of a tornado because I had the best chance of getting the message at the right time. There is no doubt that sirens should be the last resort, but sometimes you NEED that last resort to fall back upon, that "PAY ATTENTION NOW!" smack upside the head. Sirens have saved countless lives over the years. Just because there are more technologically advanced methods now doesn't mean that sirens have no more value. Any method can fail and we need all of the alternatives available to reach as many people as possible.
We need all of the warnings we can get and getting rid of sirens is taking away a big one that the population is already trained to use and understand. If people can't hear the sirens, we should consider more, possibly smaller and more targeted ones to supplement the big ones. The technology that exists now means that you could probably make smaller, better featured sirens for much less money than we spent in the past on those giant ones. Maybe we should consider that rather than just getting rid of them?