The line remained open serving first Kincardine power station (full name Kincardine on Forth power station), and then also Longannet power station. The line through Kincardine was still open in 1978 when I worked in the power station. At some point after that the line beyond the power station as far as, I think, Cambus Junction became OOU and any power station (both of them) traffic came in from the east through Dunfermline and Culross.
The section from Cambus Junction to Stirling became OOU when molasses traffic to Menstrie ceased in 1991. The whole line between Stirling and Kincardine reopened in 2008 when passenger services to Alloa started, and merry go round traffic to Longannet power station (Kincardine having been closed and demolished) started using the route. This meant heavier trains, as previously coal trains were routed over the Forth Bridge which had weight restrictions.
The well-known railway author Derek Cross, from Ayrshire, had an extended article in the Railway Magazine in, I would guess, 1973 about riding in one of the Merry-go-Round trains from Ayrshire collieries to Longannet, 2xClass 20 hauled, and that was routed directly via Stirling to the power station, continuing empty after unloading, through Kincardine station site, to Dunfermline to park overnight. There must have been some reason why the line west of Kincardine was closed and these trains were sent the less convenient and roundabout route via the Forth Bridge, and getting in the way of the high speed Glasgow to Edinburgh service.
By chance I saw such a train, helping to recall all this, just months afterwards in Glasgow, climbing from Bellgrove up towards Springburn, and as the article described it was noisy full throttle and little more than walking pace up the steep gradient there. The underpowered operation was the complete antithesis of Merry-go-Round operation, despite the modern air-braked wagons; it had been assembled all the previous day at the colliery by a shunter, a wagon at a time, took the next day for this single trip, including a crew change at Cadder yard, and came back empty from Dunfermline on Day 3.
