Thing is, Ke$ha is a song writer for Dr. Luke, etc. I believe. So even if her songs fail to be successful, she'll still be in the music industry, writing songs for other artists. So she can always feature herself on a song, if she's writing the lyrics.
But as others have said, Blow has been a massive top 10 hit in the US, so she's in a good place to continue her career.
Blow also re-entered the charts recently for a few weeks in the UK, since a remix of it was used in the Inbetweeners music, and it was also used on Big Brother, so it got back in the top 100 again for a while. So it hasn't done as badly as it looks.