Hello and welcome to JustAnswer,
unfortunately, since i am not a spine surgeon, i can not get into the benefits or downside of either procedure. however, i CAN tell you this.
what you want for your father is for the disc protrusion to be isolated and easily reached by an operating scope. this would allow for the microdiscectomy.
a fusion is typically done if there is instability in the lower spine along with the disc protrusion. AND, if a fusion is needed, then each spine surgeon has his or her favorite procedure to do the fusion.
so the first question would be if a simple procedure like a discectomy will suffice. the recovery is simple.
he wants to avoid a fusion if at all possible, especially at his age, as it comes with many complications and once a segment is fused it is nearly inevitable that, sometime in the future, he will get another disc herniation and might require another fusion. before long he is worse off than he is now.
so, i don't know if i answered your question, but before agreeing to a fusion, i would ask very specifically if a less invasive and debilitating procedure can be done. also, if he has not had epidural steroid injections these can often provide great relief and buy time for the problem to resolve over time. most disc herniation pain resolves in a six month period.
these questions, and they are all good ones, should be directed to the spine specialist he eventually sees, but again, if a fusion can be avoided it should be.
does this answer your question?