SNCF (French railways) was responsible for getting you to your planned destination and was obliged to offer an alternative. If they didn't do that (did you ask the staff?), then they should reimburse you for any reasonable costs you had to make to arrange this yourself.

You can get a compensation for delay from Eurail via this form:

https://www.eurail.com/en/help/delay-compensation

thanks for your reply.  Problem was staff couldn’t say when trains would be running again. There was absolute turmoil in the the station with announcements only being provided in French (i suspect these were also being provided on the train down from Paris but we didnt know because as in French - unlike Renfe in Spain who do all in Spanish & English which is much appreciated.

The station staff were doing their best in a difficult situation made worse with a baggage scare causing evacuation of the entire station for a while.  

Given there was no timeframe for the next train and limited bus tickets available (and with the planned national strike day the next day) we just just grabbed the last couple of flixbus tickets we could which still didn't get us in to San Sebastian until after 8pm. 

The only suggestions from the staff were either take the train back to Paris or wait and see whether the 5pm train to Hendaye would run (which wouldnt get us into San Sebastián until probably well after 9pm).  Hence the decision to take the bus while we could.