I haven’t tested but I’m pretty sure the data would be there. The databases containing them are after all just files.
That done not mean that it would restore correctly, of course.
If you had your client set to delete your messages from the server after you downloaded them, you’d lose any downloaded since the last backup. If you left them on the server, they might or might not re-download.
Making a backup using Deltachat’s internal UI, and using it to add the new iPhone as a second device, would be reliable, and would certainly get all the missed messages (in the last month or so) from the server.
If you were willing to test macOS’s backups, using a DC backup as a backup-backup, then posting the results here would be really useful to others with the same question.