theres an easy way i found out.. Instead of waiting i save my game after beating A treasure boss and turn my ps2 off and on then boom its there again! Well it was always there for me for some reason try it! it might work for you.
If that does work walk to another far treasure boss and beat it then walk back to that place it should be back.. Make sure every tresure it gone form the chest.!
To be a rock and not to roll -Led Zeppelin Marth Owns Old school style. STYX!!
There must of been a door there in the wall!
treasure bosses comes back?? but i never seen any treasure bosses respawn. other than the one in moutain path. it was a turtle + 2 snakes monster then later rock golem was there.
They might not come back if you don't take all the treasure(say, you left the crappy medicines or Worn-Out-Armor or something). Other than that, every treasure boss respawns infinitely, my guess is about 30 or 45 minutes in game time after you emptied the treasure chest.