Hmmm. It'll certainly take on that meaning for us fans one day.
But still I can't imagine Mark writing his OWN "goodbye" song from the perspective of someone else. That would be a very odd thing for anyone to do, wouldn't it?
Besides, if that were the case, he'd also be singing his own praise (his "light would keep on burning", his "song would keep returning"), which for me just isn't compatible with the Mark that we (think we) know.
On top of that, he says he wants to make a few more albums, so for me it's not a swan song, but a goodbye song to someone.
From my end, it's clear that the character in the song is addressing someone else, whose "soul is heading to its rest", and it's their "light that will keep on burning", and their "song that will keep returning", not his own.