My wifi icon disappeared, but I am connected to the Internet. How do I get it back.

Have you tried restarting or resetting your iPad?

Restart: Press On/Off button until the Slide to Power Off slider appears, select Slide to Power Off and, after the iPad shuts down, then press the On/Off button until the Apple logo appears.

Reset: Press the Home and On/Off buttons at the same time and hold them until the Apple logo appears (about 10 seconds). Ignore the "Slide to power off"

Probably not on. You can be connected to the internet also without WiFi when you have the iPad WiFi+3G.