Could 8s-8 be simplified to just 8, or is that simplest form until the value of the variable is stated?

It is the simplest form until the value of the variable is stated.

8s-8 is the simplest answer if you are saying 8s-8 equals a variable in most cases y. If 8s-8 equals a number like zero then it can be simplified again. For example 8s-8=0 is also 8s=8 is also s=1, if you have 8s-8=y  then that is the most simplified u can do