Local Voting after Brexit

While British ambassador Simon Manley has been trying to put out the fires of health insurance, pensions and the falling pound (see his latest address to the Britons in Spain here), no one wants to talk about the British residents in Spain and their voting rights in the Spanish local elections of May 2019. Will they be able to vote then? Will they be able to put forward candidates? Without the British, will the Town Halls concern themselves over the remaining foreign residents? Will Spain and the UK make a special bilateral agreement on local elections (allowing Spaniards to vote in the UK and Brits to vote here)? Is anybody talking about this? Is anybody listening?
I was approached today by someone who wants to look forward to the next local elections. What could I tell him? We may have the vote, or maybe not. For our town, where the population is roughly split between the local Spaniards and the foreigners, these concerns are huge. Our mayoress would likely win the next elections anyway - she has formidable advantages -  but would she have a token foreigner on her voting list? Would she spend energy on those concerns that the foreigners might have? Would our British opposition leader (born in the UK, been in Spain since she was three) be able to run her party? Yes, she could take Spanish nationality, but what about her voters?
Spain has an agreement with EU countries that expatriate EU citizens can vote and be voted for in local (and presumably European) elections. The European elections, by the way, couldn't be more useless here as candidates, operating on the same list system, represent their country filtered through their party. You either vote for a conservative Spanish nationalist or a socialist one. Neither of them could care less about foreign residents' rights.
Spain also has bilateral agreements with a number of other nations. These include, I think, New Zealand and the Turks and Caicos Islands. In these cases, the suffrage is merely active. You can vote (yes, both of those Kiwis, I mean you!), but, you can't run for office. Can we expect to be given a sop along those lines?
I can't see the British allowing the Spanish residents over there the right to stand in any elections if the Brexit gave them an opt-out, so would doubt that we would retain those rights here.
Either way, it is beginning to get close to the time when new parties are formed, new alliances, new candidates and new proposals. With Brexit, we may be facing the loss of even more of our rights as foreigners in Spain.
Simon Manley touched on this concern in a note issued on Tuesday September 12th: '...On the right to stand and vote in local elections, the UK wants to protect existing rights of UK/EU citizens to vote and/or stand in local elections in their host state. However agreement has not been reached on this point...'.
Well, when are the next local elections in the various EU states and what would happen to existing foreign councillors when the Brexit finally bites? We need some information and, of course, some proper representation.