Dont think it means that the vow disappears. But there is no
need to rely on it.
http://www.purifymind.com/PureAction.htm
Bodhisattvas make vows until they reach the eighth bhumi, or stage,
of the Bodhisattva Path -- the position of non-intentionality. At
this stage, they help sentient beings spontaneously. Once they
attain the eighth bhumi, bodhisattvas no longer need to make vows.
Here's an analogy: you may vow to climb a mountain, but you don't
have to repeat the vow once you reach the top.