''We do still have E111 cover until Dec.''
E111 is now EHIC, and yes, only until end Dec.
To all the 'you just have to get travel Insurance' - yes, that is fine, if you are young, if you do not have pre-existing conditions or chronic illness, if you do not need dialysis, etc. For the others, it will be either VERY expensive, or not available at all.
So imagine you have bought a little place in France, or your children live there- within a few hours travel- and you have any of the above, which would preclude you from having travel Insurance- with EHIC, you could still go- and be covered, but would have to plan to cover repatriation- be it by plane, or by car with one of your children, relatives. Even if they have to hire a bigger car so you can be more comfortable, the cost would be relatively low. From next year- you may not be able to visit them any longer.
Imagine too, that the EU/EEA country you live in does not have travel insurance products- as is the case for us. What then?
And if I may, Australia is not really relevant to this thread, we are talking about EHIC reciprocal cover here.
As for driving- and again, we must not mix tourists and residents here- about the situation in Ye Olde Days pre EU. You had to retake your licence again, IN FULL - in the local language. You had 6 months to do so if becoming permanent resident (as I did in 1970) or 1 year if temporary resident. I can just imagine all these elderly UK EU residents having to retake full licence in their country of residence, in French, Spanish, etc. It is not planned- but that was the case then.