If it goes back to the House, there are needed only about 18 republicans to vote with all the democrats to fund Obamacare.
On the other hand if Cruz is successful in getting 41 Senators to vote no on cloture, then Reid will have to with hold a vote on funding the government without Obamacare or shutting down the government.
This is why it is essential that republican senators and some democrat senators join Cruz in voting against cloture. It puts the onus all on Reid. This is a sound strategy if the republicans in the Senate fight with Cruz.
The Rino's in the Senate don't have the stomach for it, imagine having to sit at the table with Obama and actually hammer out some changes to Obamacare, when will Reid, Obama and Pelosi for that matter get it...