I don't think the petition "forces" a debate, it's not that kind of petition but it should influence policy change.
Three new EDMs, petition, motion to kill the whole TPD etc etc -- it all helps and worst case scenario is blind eyes turned to "infringements" and hopefully an early review of the TRPRegs.
If (I think it's a big if) the TRPR was "killed", the law simply reverts to prior TPD Regs which don't cover "e-cigs".
Then, the Govt might decide to introduce specific regs or an SI to control aspects of vaping devices and liquids or simply announce that these would be covered by existing legislation.
If the TRPR is "killed" the UK could be fined by the EU for an infraction.
All exciting stuff though and the vaping profile certainly has been raised by all of this following on the heels of the RCP report and Lords debate.