Ioncube obfuscation is 1-way hashing proc of values.

Classically there is no decryption of such values, have you heard somewhere about hash decryption (sha, md5)? It is naive to think that this is possible when it is the encryption standard and accepted security baseline in many areas of IT.

No matter how it may sound at first, some recovery techniques do take place, its also the same classic mechanisms, and its do not imply a complete recovery of all values of a given segment, rather partial, in some cases a complete recovery of the original values is possible, it all depends on the amount of working information available.

One way or another you can cover all the php functions except for the whole range of user values, user values are infinite and you don't always need them. It has synchronous dependency and you can change them to whatever is convenient within the scope of the task.