Just looking at the numbers, I have no idea how it could manage not to. Let's do a worst-case scenario for Twilight Princess here: no player's choice release, and no sales from new areas that the Wii launches in.
So far in 2010, Twilight Princess has sold 297,000 copies. In the same period in 2009, it sold 269,000. For the rest of the year from now, Twilight Princess sold 80,000 copies last year. That leads us to Twilight Princess selling around 80,000 this year too.
However, Twilight Princess is doing far better right now than it did at the same point last year. For the last 4 weeks, it has sold 32,000, whereas last year it sold only 19,000.
If that ratio is maintained, it means Twilight Princess would sell 130,000 for the rest of 2010.
As TP needs 310,000 to best OoT from right now, that means it's going to need somewhere between 230,000 and 180,000 more after 2010.
Now, how hard will making that be? The most obvious comparison is Phantom Hourglass, and how well it sold after The Spirit Tracks came out.
When The Spirit Tracks came out, Phantom Hourglass had been on the marked for roughly 130 weeks. For the 52 weeks before the Spirit Tracks came out (week 80-130 for Phantom Hourglass), Phantom Hourglass had sold 160,000 copies. For the 40 weeks since then (week 130-170), Phantom Hourglass has sold 150,000 copies. In other words; it actually sold slightly more after The Spirit Tracks released. It either received a slight boost, or wasn't changed at all by it.
Or for that sake, let's take Super Mario Galaxy, as it's on Wii. It's sequel released in Super Mario Galaxy's week # 135, in late-May 2010.
For the 21 weeks (from the start of 2010) before SMG2 launched, SMG sold 208,000 copies. For the 21 weeks following it (which doesn't count any weeks that have a holiday boost), it sold 391,000 copies.
Nintendo titles have the amazing ability that sequels don't ruin the predecessor's sales. In fact, they tend to boost them. I'd be willing to bet that Twilight Princess will sell more in 2011 than it did in 2010.
I'd say Twilight Princess should pass Ocarina of Time sometime in late Quarter 3 next year. Its total sales by the end of next year should be around 7.8 million, and it should pass 8 million before all is said and done for the title.
Edit: Oh, that "a bit over 8 million" estimate is also assuming that there isn't any player's choice release, and that Twilight Princess doesn't receive some sort of re-release in other countries. With those (which by all means are very likely to come), I'd say 8.5 million doesn't seem unlikely.
On a completely separate note, I wonder how much Ocarina of Time will sell all versions combined. The Master's Quest edition is sure to have sold a million, then there's the Virtual Console release which has definitely passed 1 million (http://www.vgchartz.com/article/4790/channel-surfing-wiiwarevirtual-console-sales-chart-july-2009/), and now there's the 3DS release.
I have no idea about Master Quest's sales numbers, but I think 1.4 million is a fair guess. That puts the "pre-3DS release" Ocarina of Time numbers up to roughly 10 million. How much can the 3DS version add to that total? If the Super Mario 64 remake is anything to go by, it could potentially make it as high as 15 million.
(Again, this has nothing to do with your comparison, I was just curious)
Edit 2: Fixed a numbers error. Whoops!
