Those seeds always made the best coriander seeds I've used. I harvested them every year
and gave up (because of the heat) growing for the leaf. As mentioned,the seeds will come back the next year but it's a good idea to keep on planting throughout the season if you want any leaves at all.
Actually, I think I began to believe that it's not just the heat but more that they respond to the longer days that we have at the 44th degree. Specifically, liking shorter days that one finds in So. Calif or Mexico. I've been noting where it does grow during the summer season.
I've always been curious. If it grows throughout the season in San Fran for example, then it could be the lack of heat even though it copes with the same length of day. If it grows in the Yukon, then it could be just the lack of heat. But if not, then it would be more the length of day. I think the combination at the 44th, given 90+ degree longer days, just doesn't work.
So where you are, you probably experience the same problem as I did.
I can never just make things simple.