Last question and it`s a go

So I decided to use re-use Pappers stove top pasteurization method with my next batch but I've never used this technique with freshly pressed cider and was wondering if you think the cider will ever clear in the bottle after pasteurization. I use champagne bottle.

I will use some pectin enzyme but will it loose it's effect after pasteurization leaving me with a sweet cider that will never clear ?

it clears, i have done it a couple times with stuff that was still a bit cloudy and it has cleared 100%. the bigger issue is getting that large thick bottle up to the kill temp

I would definitely recommend having a tester bottle filled with room temp water and a thermometer probe in there for each batch to make sure you got the right temp. Bottle bombs are bad enough but champagne bottle bombs are another story entirely that the pressure they will carb to before exploding.

what is the temperature I have to reach and for how long in order to be 100% sure that all yeast are dead ?

i can't vouch for the absolute accuracy of this, and every yeast strain is going to be different, but this has been posted before and seems to work as a general guideline
at 53C = 128F minimum time to kill population 56 min
at 60C = 140F minimum time to kill population 5.6 min
at 67c = 152F minimum time to kill population .56 min
but that means that the entirety of the liquid needs to reach that temp. when i have done this i aim for 70 deg