Is there something ambiguous about the result? Quoth Vriska:
I won't make you do it. This is up to you. Here's your chance!
8ut do it fast, ok? Please don't make me 8leed to death slowly.
And we saw earlier that she later says to Tavros:
You couldn't even do the one little thing I asked you to! The one thing that would have made you man up once and for all.
So instead you flew away and cried, and decided to sleep away your sorrow for the rest of the adventure.
It seems pretty obvious to me that Tavros will fly away and cry and Vriska will 8leed to death slowly.
Then again, it also seemed pretty obvious to me that the indestructible demon that messed up the troll session was the indestructible demon known as Lord English, and that has been confirmed as deliberately left unconfirmed.
As for why she doesn't just force Tavros into stabbing her, well, I think having a crush on him is reason enough. She wants Tavros to man up, be strong, and commit his own murders.
EDIT: DAWNING REALIZATION
Which is kind of what he's doing in the future. ._.
I know she's since moved on to John, and then moved on to Nick Cage, but I can't shake the feeling that if Tavros ever gets to Vriska's lair, there's going to be more kissing.