My iphone 4s is stuck on a black screen?

Six hours ago my phone froze on my text messages page. This has happened to me before and I know typically the solution is a hard reset but I recently broke my lock button (it doesn't work at all) and so I just had to let it die. It was at like 60%. Siri was still working so I told siri to call my friend to help the battery run out faster. My friend accidentally hung up because he forgot we were on call and he locked his phone, and after he hung up the screen went black. I did this around 30% which was like four hours ago. Siri was still working so I figured I would just keep checking to see if it was dead by pressing the home button and listening for the noises siri makes. But it's been literally four hours. I don't understand how the battery isn't dead? This is beyond frustrating. I really don't want to put it into DFU mode. I just want to know basically if my phone is doomed (I've had it a year and a half) or if I just need to be more patient and wait for it to die.

First off, you won't be able to put it in DFU mode if your power button doesn't work. So what I would do is plug it into itunes and try a restore. If that doesn't work, if you are comfortable messing around inside the phone, I would remove the battery and then put it back in and see what happens. It should reset it and removing the battery is a pretty simple task.