Is there any way to get a sequence diagram from a communication diagram?
Currently there is no way to generate a sequence diagram from a communication diagram, or vice versa.
Communication diagram is kind of Interaction Diagram and reuses some UML elements from Sequence Diagram, but is very limited. Most of advanced Sequence Diagram elements can't be reflected in Communication Diagram. It includes all kinds of CombinedFragments, Gates, Nested activations, Sequence of messages and more, so even theoretically Communication Diagram can't be equal to Sequence Diagram.
Currently we try to gather information what would be the benefits of this feature. We would be very grateful if you could share your opinion with us.
For non automatic elements reuse - Communication Diagram can be generated inside the same Interaction (as Sequence Diagram). In this case Lifelines can be reused by simply drag'n'drop them from Interaction directly to communication diagram.