Will they fall out after a year?
No, if they are going to fall out it will happen long before then.

will they damage new pedals?
No, the pedals will thread into the new helicoil threads, which are the correct size and undamaged.

can i then when need to replace chain set be able too take out the pedals and put into new chainset?
Yes. Locktight the helicoil to the crank, and apply anti seize lube to the pedal threads.

will performance of bike be affected?
Only if the repair is not drilled "straight" or it works itself loose.

I've used helicoils on other things (mostly cars or machines at work) with good results, but never tried them on a bike crank. I'd like to hear from someone who has. I think as long as the repair is done properly, it will be fine.