Killing the troll is not the only answer. He is camped out on your corpse because that is the last place he saw you. Eventually he may wander away; eventually you may win the lottery.

What I would do is lead him away from the corpse. Given your situation, I would cross the river upstream or downstream out of his sight. Circle around to approach the troll/corpse location from the side opposite the river. Then get his attention.

Once you have his attention, he will chase you. You need to keep ahead of him while remaining in his line of sight for at least a hundred to a hundred and fifty meters. Then find rough terrain/a wooded area where you can break his line of sight and sneak away from him.

Once he has lost track of you, he will remain where he is. Circle back around and pick up your corpse.

You will learn how to kill trolls efficiently as you progress. The idea is to stay alive while doing so.

Note 1: It is entirely possible that you will aggravate other enemies during this process. Don't panic. Lead them away from your corpse also. You should be able to pause long enough to kill them off a little at a time.

Note 2: This strategy will be useful against bosses and other enemies also.