If there anyone with any less momentum than the Ontario NDP its the Ontario Liberals who are currently polling in third place and would lose four fifths of their seats if an election wefre held today. ONDP support is averaging 23-24% whihc is exactly what they got in the last election.
It would be nice if the ONDP won the SSM byelection, but even if they don't it won't change the fact that Horwath will be leader in the next election. She is currently (albeit by default) the most popular provincial party leader with by far the highest net favourables. Wynne will likely stalll calling SSM for as long as possible meaning she probably calls it in late June for August 2017...that that point we will already be within 9 months of the May 2018 Ontario election and there will be no mechanism or will in the ONDP to both find a way to depose the leader (there would have to be a convention happening for that to happen) and then have a six month long leadership campaign whihc would basically mean picking a new leader a week before the writ would drop for the next election...not a chance.