this sentence to indicate the two events linked to each other,the first sentence the condition to occurrence of the second sentence. so we use the tool condition كيفما /ما the condition in first sentence is "will be" so we use كيفما /ما as a condition to occurrence of the second sentence "Whatever" and mean Whatever in this case is كيفما او ما كيفما يكون سيكون or ما يكون سيكون Whatever:كيفما/ما will be:يكون(when we usedما/ كيفما with يكون that refers to the future) will be:سيكون

كيفما يكون سيكون or ما يكون سيكون there's no a short way to write it

I think the word "whatever! = !أيا يكن" has the meaning of your sentence... But we also has a very common phrase which I think means exactly the same as yours It's "sho ma kan ykoon = شو ما كان، يكون" (in Syrian Arabic) and "ayian yakon yakoon = أيا يكن، يكون" (in MSA) We use this sentence to indicate that we will do something without caring about its consequences. E.g. I'll do it and whatever will be, will be = سأفعلها وأيا يكن، يكون

All of them right but you can say like that : ما هو كائن سيكون this is the best and shortest you can say it or you may say it : سيكون ما هو كائن في وقته

ما سيحدث .. سوف يحدث