thanks

he will be there untill you kill him

He will stay there until you kill him, and he also regenerates HP passively.

He's waiting for you the game doesnt run when you log out lol
There is at least 3 new Elder temples you could go to other than the one you have spawned.
dig a trench if you need it and clear the area a bit, hide behind the posts and trees shoot fire arrows the best and just have a ton of arrows the Elder is quite easy to do.
This is exactly how I did him but made a smaller tunnel with ramp, that deep is not necessary just go under the base. Take your time have plenty of food and be patient.
https://youtu.be/gKTH8ZP0Fas
Maybe ask friends to help in the Valheim discussion hub pretty sure some will be happy to help out. Depending on their country and time zones.