Gothmog and the Mouth

[Inziladun]

Originally Posted by Ghazi

There's no evidence to suggest this but I wonder if Gothmog was the last king of Gondor, Eärnur. He foolishly rode to Minas Morgul and was never seen again by the good guys. I wonder if he was whisked off to the Houses of Lamentation that were mentioned by the Lord of the Nazgul, or used in some other way.

Granted, Eärnur's ultimate end was unknown, since there were no witnesses to his death, but I don't see what mechanism Sauron would have (other than the Nine) of prolonging his life for so long.
And how would he have 'turned' someone like Eärnur to his service, again without making him a wraith through use of the Nine?