Your computer can get to POST w/o RAM and nothing would bad would happen if you did that. With a case speaker or mobo speaker connected, you would hear a series of beeps (1 long, 2 short), indicating that their is no RAM or there is bad RAM.
Also, w/o RAM you aren't going to see a display on your monitor.
As for the CPU concern...
On a cold boot, your CPU temp is approx 30 degrees, give or take a couple degrees. By design, the CPU is designed to shut itself off in the event of an overheat, and 5 seconds isn't nearly long enough w/o a fan to cause the CPU to overheat. I've loaded into windows w/o a heatsink fan connected and I didn't fry my CPU.