The blotches will probably spread, turning the whole leaf prematurely brown and shrivelled, as is already happening to this tree in the city centre:
In 2006 after losing their leaves prematurely some trees were observed to flush and even to flower in autumn.
About this time last year I took a bus journey across Bedfordshire into Cambridge and passed countless Horse Chestnuts with almost no green left on them – the route was unrelieved by a single healthy tree. My impression is that this process is slower this year, so perhaps our reasonably chilly winter slowed down the moths’ emergence, or else management techniques are working. (Management might explain why the tree in the park is doing better than the second one pictured.) According to the Forestry Commission the leaf miner is primarily an aesthetic problem and thankfully there’s no evidence that it damages the trees in the long term. Bleeding canker is a more serious problem for this species, but even so the leaf miner has only been in this country since 2002 so it might be a bit early to say that trees won’t be affected by dropping their leaves months early in successive years. The Horse Chestnut seems to me a particularly urban tree as so many grow in parks, school grounds and gardens. The sight of its large, soft leaves drying and curling back as though scorched is unsettling and yet it's already beginning to feel like part of summer's rhythm.