The car will over heat.
a leak is probably getting on something hot and cooking away
You can, so long as you monitor your coolant level. You'd be best advised to have the leak repaired ASAP.
there might be a leak some where in a coolant line. or maybe you have a leak in your radiator.
It depends on how bad the leak is .If its a really bad leak to the point where the car is starting to overheat then no
You have to determine the source of the leak then decide on how to fix it.
cap is off
water pump
Low on antifreeze/antifreeze leak...loosenut... www.ceriousproductions.com
You will need to replace the heater core.
Antifreeze leak top of engine
You would have a leak, from either the pipes to the heater matrix (radiator), or the matrix itself.
You need to have your antifreeze up to par and if it is a leak you are worried about until you get somewhere to have it fixed there are quick fix solutions such as Barr's Leak that you can use it will seal the leak temporarily to get you to where you are going. Do not ever open your radiator cap if your car has been running - only open it when it is cold.