Shadowmere fell off a cliff and died. How do I get him back?

I was riding Shadowmere near Alftand and I accidentally fell into that canyon near the abandoned tower. The fall was enough to kill Shadowmere.

I have done a lot of quests and other things such as fast travel, waiting, and sleeping so I am wondering if that interrupted his respawn. Also if I come back to that point before he respawns, is that bad?

Can Shadowmere just go away and never come back after his death?

I tried waiting in-game for 11 days in Solitude and then returning to Shadowmere's death point, but it did not work.

I do not want to use script commands because I consider that 'cheating' and I don't want to cheat.

According to the wiki, you should wait 15-20 days for Shadowmere to respawn at the place he died.

I lost Shadowmere while fighting a dragon. He attacked while I was riding. I dismounted to show him what was up and got hit by one of those fly over breath attacks they do. i turned to watch him and saw Shadowmere flying of into the distance. It sucked to lose my buddy but it looked pretty funny. Anyway, around fifteen days later I did a fast travel and there he was just waiting for me. I was pretty happy to see him again. He is pretty awesome!