Anderson is on his own pedestal as regards to his MMA legacy already. Sure, losing would smudge his unbeaten UFC record and his aura of (recent) invincibility, but nothing, I think, will knock him off that exclusive perch.
I disagree with the statement that a win over Jon Jones wouldn't be a major addition to his reputation. The word legend gets thrown around a lot, and usually too casually. If Silva were to beat the New Phenom that is Jon Jones, a man that has crushed an entire division, and made it look easy, without even cracking the age of twenty five, if Anderson were to beat this Champion at a heavier weight class he might be able to cement himself as the best ever in the sport, when the sport is only in its juvensescence.
That would make for legend.