#4 This loss actually improves The Fiend character
Remember The Undertaker back in 1990? Like The Fiend, he was also an unstoppable monster who couldn't be beaten. He tore through the WWF and the only times he lost were by count-out or DQ. He was an absolute juggernaut.
And that gets boring after a while.
Eventually, Undertaker began to actually lose a match or two. It wasn't often, but it happened - and it made for a more interesting Undertaker. He didn't lose that aura that came with his character that he had earned over the years - but knowing that he could actually be beaten made his matches that much more suspenseful and entertaining. In the long run, it helped make him the legend he is today.
Of course, the early 1990s were a very, very different time than now, but the same psychology still remains. As great and unstoppable as The Fiend has been, having him this great and unstoppable over an extended period of time would just get, well... boring.
Losing to Goldberg isn't burying The Fiend. There's all sorts of ways you can take this character now. How will he respond? Did he lose on purpose - as part of a more diabolical plan? Are the two sides of Bray Wyatt at war with each other?
Hey, remember when Bray Wyatt's swamp dwelling cult leader character just kind of did the same thing over and over? We could just be dealing with that again.
One final note for the armchair bookers out there: One loss does not equal a burial. So, stuff it,