I had a feeling The Bee Gees would comment on Paul's situation and I found backmasked references to him in The Bee Gees song, I Started A Joke, recorded on June 25, 1968 for their Idea album.
The forward lyrics suggest that the Paul-Is-Dead rumor was a joke but that Paul did die sometime between the beginning of the "joke" and the recording of the song--a variation on some of the theories. The lyrics say Paul "fell out of bed, hurting his head." I'm staying with the theory that Paul suffered some sort of accident, but survived it.
The backmasked lyrics say:
0:07-0:26 Paul, he moptop
0:44-0:47 Given up [his?] quest
1:15-1:17 He moptop
1:36-1:38 Given up [his?] quest
2:06-2:08 He moptop
2:32-2:33 He moptop