[Rez]

The solder will conduct. You don't want to leave the legs behind because they'll just be in the way and might result in a weak joint.

You need to be very carefull when soldering FETs or any other solid state device. If you get them too hot you will burn them out before you finish. Soldering wires is one thing, soldering solid state, especially surface mount, requires good equipment and skill. PRACTICE FIRST.