Is it permissible to combine Dhuhr and Asr prayers without shortening them, upon returning from a long and exhausting journey, knowing that one will not wake up until after Maghrib or Ishaa, and what is required concerning what was prayed in this manner three times?

You may combine Dhuhr and Asr prayers out of necessity and hardship, such as extreme fatigue from travel. This is based on the hadith narrated by Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace be upon him) combined Dhuhr and Asr prayers in Medina without fear or rain, so as not to cause hardship to his Ummah. This indicates that the basis for combining prayers is hardship. However, if there is no hardship, then combining is not permissible, and whoever combines must repeat the prayer. If you sleep and do not wake up until after Maghrib or Isha, you must make up the Asr prayer, and there is no sin upon you due to the excuse of sleep.