06:50 Enterprise Delayed 17th Nov
 

The 06:50 arrived into Newry at 07:51 and now we are waiting! A tree has fallen on the line somewhere between Newry Station and Dundalk Station. This is all we know so far. We have sitting on the train in Newry for about 15 minutes now.

Train conductor is taking a head count - presumably we will be getting bus transfers. The 07:35 from Dublin apparently cant leave Dundalk either - we have been told there is more than 1 tree down.

Translink website is reporting that the train has terminated at Newry and passengers will be accommodated on the 0800 Central-Connolly, which will presumably now be making extra stops at Dundalk and Drogheda.

we were transferred to 08:00 which was 15minute late to newry. just stopped at dundalk.

That must mean a 29K on the 0935 from Connolly although not reported as such anywhere on the internet

Summary
06:50 - Belfast to Connolly terminated at Newry.
09:05-09:10 - Passengers from 06:50 transferred to 08:00 at Newry
10:31 - The 06:50 and 08:00 passengers arrive in Dublin Connolly

Is a fallen tree enough excuse for IR/NIR not to issue refunds on the basis of it not being within their control?

Doubtful. Passengers on the 0650 should get a 50% voucher rebate (60-90 minutes late) and those on the 0800 should expect 25% (30-60 minutes late).