1) The "Dragon's Teeth" tank traps are a CADW protected ancient monument which is why they are still there.
2) Houses are not "uninsurable" in Fairbourne. I know, I live there and I have house insurance.
3) Network Rail can't plan for beyond their current ORR Control Period, so what happens post 2054 (the 40 year commitment to maintain defences given by Gwynedd in 2014) is way beyond the ability of the organisation to plan that far as it is several Control Periods into the future. Also, in the Welsh Route Utilisation document, whilst the Aberystwyth line is defined as a "main line" the line along the coast has the lesser "rural branch" designation. If the line became too expensive to maintain (and aside from Fairbourne there is coastal running at Tonfanau which despite rock armour was breached a couple of years ago, the coastal wall at Llanaber north of Barmouth was destroyed at the same time, and further north beyond Criccieth the line is at risk of inundation) would the Welsh Government have to take the difficult decision to close the route?
4) I've been actively involved not only as a resident but as a former Community Councillor for the village and in the initial action group set up by the residents when this all kicked off and things are not as black and white as it seems. However, the future of the rail line hasn't really been considered and it's not Gwynedd's responsibility to look after it, so the future of the Cambrian Coast line beyond Machynlleth, whilst politically might be seen as safe, actually isn't simply because the industry funding and regulatory frameworks don't look that far into the future.