Week 9, day one. C9 vs. TDK.
With C9 all but guaranteed to miss playoffs after going 0-2 this week, this split's winners and runners-up are both likely to go to Worlds. The only way the runners-up wouldn't have enough points to qualify directly would be if Team Liquid came 3rd, in which case they'd go.
Qualification for the gauntlet tournament to decide the 3rd spot is going to be really interesting during playoffs. C9 may well end up making it in at the expense of a beaten quarter-finalist thanks to their runners-up finish in Spring.
Actually, unless TSM comes in 1st place (and thus takes the automatic spot), there's very little chance of anyone else qualifying through on points. If TSM finishes at 5th or 6th then C9 can beat them with a 2nd or 3rd place finish (this is obviously very unlikely), or CLG can beat them with a 2nd place finish. If TSM finishes in 4th place or higher, then only C9 could beat them on points, and only by finishing in 2nd.
The more interesting situation actually occurs if TSM finishes 1st, because then there's actually a wide variety of circumstances where different teams can manage to qualify. At the moment, though, Dignitas, Impulse, Gravity, and Liquid basically need to finish 1st place to get one of those guaranteed slots; the Vegas odds are you're going to see all four of them competing in the NA Regional Qualifier, possibly with C9 taking one of those spots.
If I were to bet: TSM qualifies via 1st place automatic finish, CLG qualifies in the 2nd spot via points, and the Regional Qualifier comes down to C9, Impulse, Liquid, and Gravity. Dignitas is the odd man out. (Along with, obviously, NME/T8/TDK.) I could see Liquid or Impulse upsetting CLG to take the 2nd spot, though, and obviously if TSM fails to secure 1st it becomes whoever
does take it, with TSM taking the 2nd slot via points.
As far as who would win Regionals out of those four teams if they played today... hell if I know. Those teams all show an amazing lack of consistency amongst one another, though obviously C9 looks unlikely to take a Best of 5 off any of them at the moment. I suppose I'd have to give it to Impulse, personally, though a strong argument could be made for Liquid or Gravity.