A few modern campaign questions

[Mr Grumpy]

Many features of these games are somewhat abstract, this is an example of that, if an engineer unit wish's to move away from the location where it has laid a bridge immediately (maybe it is in danger of being cut off) then it can abandon the bridge rather than going through the "bridge ops" procedure, there is no explanation in the manual as to what happens to the bridge it just disappears. 

As we know the big downside is that unit can no longer lay bridges in the remainder that scenario.

The "abandon bridge" feature was added after several titles had been released, I assume because players complained that they were losing the engineer units as they were locked into their location by the bridge ops feature.