Again, thanks for your response.
I knew the 1:200.000 KuK maps, it always amazes me how precise they are considering when they were made :-)
Here is a piece of KuK 1:75.000 - actually a Czechoslovakian map updated in 1925:
Obviously bridges in Sighet and Bocicoiu are still there, altso the narrow gauge railway can be seen. Basicaly same as the 1:200.000 map you posted.
Then there is 1:200.000 Soviet military map. Both pieces of shown below are officially updated to 1978. They could be out of date "from the start", ie. even then, but the bridge at Sighet is still there (still no road bridge), and there is no bridge in Bocicoiu Mare.
That's pretty much all I know for sure about this. It would be cool to learn some more
Also the Panoramio photo of the Velky Bickiv bridge (which I posted above) and the fact it looks very much like the debris that can be seen in the water in near Bickiv, might indicate, two things:
a) at some point before the bridge was destroyed it was turned to road traffic,
b) that it was not destroyed on purpose (it's only speculation, but 1998 flood have made great damage all over the Carpatians).
Obviously the trace of the railway can be clearly seen form the train window when passing thru the Bocicoiu Mare, but this doesn;t tell much about when it was dismantled
The date of closing / dismantling of Sighet railway bridge might be somewhat traced by checking when the line near Sighet Camara was made "straight", without crossroads (I have no way of checking this, my Romanian is way too weak to ask any of the railway workers in Sighet).
As of last July on Ukrainian bank the railway towards the place of the bridge still existed (it was visible from the train). However I don't know if it was usable.
From what I know the line to Velki Biczkiv was meant as an alternative to the line on Romanian bank, and it was built in Soviet times. It seems that line was "formally" built up to Bila Cerkva - it the farthest passanger traffic station in this line that I know of (for example it's still on the timetable of UZ, despite the fact that no trains go there). The same story says that of line was not finished (not reached Rachov) because of financial reasons.
I also read somewhere that in 80's there were transit trains from Teresva to Rachov through Romania, on the wide gauge, only for local inhabitants, and only with some kind of permit.