You can call your pet after receiving the roll effect, the bonus will still apply.
If you Release and then summon another Avatar, your pet accuracy bonus transfers on that new pet.
Busting on Drachen Roll does not bestow a penalty on your avatar's accuracy, according to the /checkparam <pet> command. This is either an oversight, a bug with the /checkparam command or it's intended under the rationale that only the Corsair suffers from a Bust and no other entity.