Most of the remaining larger Maine customers are on the main lines and/or near serving yards like Rigby or Northern Maine Jct, so I would imagine that CSX has no intention of letting their business slip away. The more marginal business, say on the Saco Industrial or on the branch to Augusta may be a little more at risk, but will still likely be serviced weekly at a minimum.
Considering Pan Am has already implemented their version of "PSR" and there are only two freights in each direction per day Ayer to Rigby going down to one is not that big of a change. They is also only one general freight between Deerfield and Ayer down from 3-4 in each direction per day when I worked there. However, for operational reasons (complexities of combining two mile long trains, commuter trains in the way, etc) you may still see two freights a day on the Portland Division. We aren't talking about serious efficiencies gained here like going from Buffalo to Albany - it's only a 100 miles.
As for what CSX thinks of the little guys, there aren't that many left. Pan Am did a good job of assisting many "back country" customers become rail served at easier locations to handle. I don't see a wholesale shedding of them, but impossible to tell this early.