ETOPS is a planning exercise to comply with the legal requirements. Once on the aircraft it becomes airmanship and practical solutions. For example: On an Atlantic crossing, if the weather at planning stage at Shannon was below the legal planning limits, somewhere like Dublin is used if suitable. However if one did suffer an engine failure and turned back, on checking the weather at Shannon and it was above limits, being closer this would be the nearest suitable airfield to land. Equally if the planned weather at Shannon at planning was suitable, but had deteriorated, it would be acceptable to fly pass Shannon and use the next suitable airfield. If you need to fly for more than 180 minutes to find a suitable airfield where you can carry out a safe landing, so be it. I don't think anyone would like to do this, and I would like to think the odds are unlikely that you will loose an engine at the most distant point from an airfield in flight.
A question then: Having suffered an engine failure, crossing the Atlantic in winter, Reykjavik is 20 minutes closer than returning to Shannon, however Reykjavik's weather is forecast at below freezing, gusting 45kts in snow showers, and Shannon is calm and CAVOK. Reykjavik is the nearest suitable, which is the more SENSIBLE...........
I was discussing Irkutsk recently about this very subject, more to consider the temperatures here. It can get to -60C, I think they were AF were lucky it was only -14C