Do I need to remove the entire mirror to install this?

The lens slides or clips into your existing mirror housing from the front — you don't need to unbolt the whole mirror from the door. Make sure you're comfortable working around the heating element connection before you start.

Will this work if my factory heater is dead?

This is the heated lens itself, not the control switch. If your heating element isn't activating, the issue is likely in the wiring or switch upstream — test your electrical connection before installing this lens.

What if I need the right side too?

This is left-side only. Order the matching right-side lens separately if you want both mirrors heated.