The mechanism for continuance of reciprocal healthcare arrangements (including EHIC) is already in place via the Healthcare International Arrangements bill which received royal assent in March 2019. This gives the UK the power to implement new reciprocal healthcare - but we await the outcome of negotiations - it doesn’t appear to be very high on the agenda unfortunately.
Spain in particular have been pushing hard to continue with EHIC for UK citizens and discussions during the passage of the bill emphasised the problems that could be faced by uk citizens with existing conditions who may find it difficult to obtain travel insurance cover.https://publications.parliament.uk/pa/b ... 55en03.htm
Short extract from the summary document:-
“These powers will ensure the Government is prepared for a number of different EU exit outcomes and is able to implement new reciprocal healthcare agreements in the future. The Bill:
●supports the UK to implement our future relationship with the EU on reciprocal healthcare. The White Paper on the Future Relationship with the EU set out that there should be reciprocal healthcare cover for state pensioners retiring to the EU or the UK, continued participation in the EHIC scheme and cooperation on planned medical treatment, supported by any necessary administrative cooperation and data-sharing requirements;”