exile compared to night

Isaiah (Yeshayahu) 26:9:

My spirit desired You at night...

Rashi:

'My spirit desired You' -- in my exile, which is similar to night... 

Immortality in the Messianic Era?

Isaiah 25:8: "He will swallow up death forever, and Ha-Shem Elo-him will wipe away tears from upon all faces, and He will remove the degradation of his people from upon all the earth, for Ha-Shem has spoken."

Rashi: "'He will swallow up death' - He will cover it up and cause it to disappear forever from Israel."

The verse certainly lends itself to Rashi's understanding, which appears to be that Ha-Shem will cause all death to cease in the End of Days. However, Rambam famously writes in his Letter to Yemen regarding the Messianic Age, that the natural order of the world will not change, nor will people, including the messiah, be immortal. Rather, the messiah will re-establish the Kingdom of David over which he will rule, then die, and his son would reign after him and so forth. How does Rambam contend with this verse? The Radak illuminates this issue, as he is a follower of the Maimonidean school of thought.

Radak: "He will eliminate and nullify death, that is to say, premature death, but not natural death. In other words, that which the gentiles used to slaughter them in exile -- that death will be nullified then. And the tears that were upon all faces, that is, upon all the faces of the people of Israel, who would cry in the exile constantly because of the evils that the gentiles would perpetrate against them -- then G-d will wipe away those tears from upon their faces, for they will have no more sorrow."