>AbMaj7, DbMaj7, CMaj7.
>This could be considered a variant on ii-V-I, since Ab and Db are the
>tritone subs of ii and V respectively.
I see this kind of ending a lot, but more commonly using a I-VI-II-V tritone
sub. Tunes like "Ladybird" use this explicitly as the turnaround.
Minor Correction: I think you meant to write b9Maj7, not #9Maj7.
-JC