Vlad can heal for a max of around 5400 without any other champion's assistance.
https://i.gyazo.com/e3d944c81668f641b7b273fcddd13073.png

Over 6200 HP, over 1300 AP.
With a more realistic endgame (no boot) build?

~4500 max heal. 6k HP, ~1050 AP.
45% CDR on both via 30% CDR runes.
Just saying :)
######Edit: Since many of you think anyone would consider using this build in a game, its not supposed to be viable. Its simply about squeezing the most out of Vlad's healing as possible.
:

(situational 5th)
--> replace with
(still get CDR+MS, but also get AP and spammable lichbane procs)