xcode simulator not coming up - reinstall possible?

This will delete all simulator info and get you back to the point where you can use Xcode/Preferences/Components to re-download the simulators and start from scratch:

1. Quit Xcode, Simulator, Instruments, etc.
2. Run in Terminal: sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
3. Run in Terminal: sudo rm -rf ~/Library/*/CoreSimulator

Thanks to Apple Dev Forum response https://forums.developer.apple.com/thread/13718

I was able to delete my simulator devices and re-install them by following this excerpt written for a user that was missing their simulator:

Open the Xcode > Open Developer Tool > iOS Simulator menu (if you get a pop up error just dismiss it). Once in the Simulator go to Hardware > Device > Manage Devices. Delete everything listed under simulator. Reboot your machine. After that navigate back to Manage Devices in the simulator and click the plus to add back your simulators. Then the iOS 8 simulators will show up. Hope that also helps you.

Here is where it came from: http://www.reddit.com/r/iOSProgramming/comments/2b9j2p/xcode_6_missing_ios_8_simulator/

For Everyone having an issue with the Simulators today in Xcode just go to Window/Devices and Simulators and delete under the Simulators Section every Simulator. Then create a new one. Hope this helps.