SLI will stick around, but the only reason I say this is now ATi has stupidly decided to start doubling up their cards now as well.
However, SLI, in my opinion, is only practical for business use for people who need to do a lot of rendering and other intensive graphic processes, who have the money to dish out for it. The same can be said for dual/quad Opterons/Xeons, sure they're gonna stick around, but they're only practical for hardcore servers and no home user in their right mind would waste money on that. I don't think I will ever recommend SLI/multiple CPUs for any consumer, ever.