I'm pretty sure the Greens will support the PCs for the time being. The Liberals are currently in no shape to try to usurp the PCs, and even if they did want an anti-PC coalition, they would end up being the junior partner. That's always a difficult position to be in (just look at the current state of the Liberal Party in the UK).
The PCs will be safe in PEI for 2-3 years at least. They're probably safer than Higgs is........