Ok, so this Katana like sword is in Bloated Man's Grotto, however, I only found out about it after completing Ill Met By Moonlight and now I can't get to it. Is there any other place I can find this sword or am I doomed?

nope, unique item to that spot.

Try waiting/playing 30 in-game day without visiting the cave. Maybe the cave resets back to the original state. The wikia says so...http://elderscrolls.wikia.com/wiki/Bolar%27s_Oathblade

Hopefully this will work, thanks.

It does reset I too got the blade after that quest but it took a long time fro it show up and the shrine of talos also took a while to show up, but yeah wait a long time and it will be there