That's not new - and it's not that you will die in 50 rounds exactly, it's just that unkillable will stop working as from round 50 and considering that the CB is hitting for several hundred thousand damage by then (on UNM), it's usually an insta-kill on the whole team. In theory it may be possible to survive a few rounds longer, whether it's an unkillable team or not, but you'd need insane hp/def numbers and decrease attack on CB.

L9753,

I set up my UK team (RT+Bushi) less than a month ago, and assumed 50 turns was the limit for CB.

So, at turn 50 CB ignores unkillable or block damage buffs, as part of his kit? And Fahrakin the Fat has something in his kit that would allow a UK team to go past 50? Am I understanding that correctly?

I pulled Fats during this last fusion, but dont see in his kit why he would be singled out. 

I am excited to see if he can help increase my damage to be able to 2 key UNM.

The thing is most of my team mates with unkillable 1 champ set up fell way down on unm is why i was wondering 

I don't know what the deal was with Fahrakin, but judging by the description in the update, there was some kind of bug, I suppose somehow linked to his passive deflecting damage onto his allies. Whatever it was, they fixed it now, so Fahrakin won't do anything special to help with the ignore unkillable at round 50 anymore. Though he's still a very good CB champ regardless, good luck with him. 

What do you mean by unkillable '1 champ setup'? 

most of my guys the ones with 1 man eater only there keys are not near as high asw before on unm the ones that have 2 are round the same 

That  is  a  setup  with  a  Painkeeper,  its  not  a  one  champion  setup.  There  are  other  parts  too,  for  example,  if  there  is  a  Skullcrusher,  he  is  part  of  the  Unkillable  too.

I have a Maneater with Painkeeper unkillable and I have to say I haven't noticed any difference - which makes sense as there is zero reason why there would be any difference.