合う => do something together N3
~こと請け合い => I guarantee ... N1
Happens next
[合「あ」]う => To do A together/mutually N4
Secondary Verb
~ひょうしに(~拍子に)   => the moment [A], unintentionally / inadvertently caused something to happen N1
場合(は) => in the event of; in the case that ~ N4
~ににあわず (に似合わず ) => ~Different from N1
Evaluate