You can usually tell if a valve has hit the piston as it will leave a very slight indentation in the top of the piston.
If your still unsure,you need to take the cams out and tip the head on it's side.Using parrafin (or similar),fill the ports up and see if any of the liquid leaks past the valve seat.Do this for all the valves,and as they leak,mark them so you know which ones are damaged.
If your confident enough to carry out the work yourself,then I'd carry on and repair the head you've got.Complete re-con heads are around the £300-£400 mark,depending on type of engine,so by rebuilding your head,you'll save a decent amount of cash.Valves are typically around £20 each,so see how many are damaged and go from there.
If most of the valves are damaged,it might be worth sourcing a second hand head.Try FindaPart.co.uk - Parts Request
Good luck and let us know how you get on.