Could they be used on the Largs branch in poor weather when the juice has to be turned off at Saltcoats to prevent arcing?
They don't turn the power off during high tides/poor weather! They just don't run any trains now.
You won't be seeing 769s in ScotRail service as they don't fit into the new fleet plan in anyway. 318, 320, 334 and 156 all to be withdrawn and brand new emus to replace 318, 320 and 334. 158s will take over the 156 routes.
Expect an announcement in the very near future for procurement of new trains for ScotRail - all via the Scottish government procurement process.