Here's a thing. If the line between St. Dennis and Par was closed to passenger traffic, with Newquay trains going via. St. Dennis, then the results for Roche, Bugle and Luxulyan would be mixed.
Roche and Bugle have hourly bus services to / from St. Austell although the buses now terminate on the road outside the bus station rather than in the bus station itself. On the other hand, Luxulyan - first stop for trains departing from par - used to have a bus service but that was withdrawn when the council last retendered its bus service contracts. Therefore, withdrawl of the St. Dennis Junction - Par trains would leave Luxulyan, small as it is, with no public transport at all.
On the other hand, how much usage would stations at St. Dennis, Foxhole and Nanpean get when all three locations have two buses per hour, spaced roughly 30 minutes apart, to / from St. Austell with one bus per hour running to / from Newquay? Tricky situation IMO.
As for trains to / from Par, the best thing to do if the line through St. Dennis was reinstated would perhaps be to use Par as the terminus and run trains Par - St. Austell - Newquay. Perhaps I am wrong with that idea but as I am not local to the line I guess I can't really talk!
Dave