Hello,
Not sure if this is a bug or feature request but would be nice to stop participant line after destroy.
@startuml
hide footbox
Bob -> Alice : hello
Alice -> Ken ** : create
activate Ken
Bob -> Ken !! : destroy
Alice -> Bob : next step
@enduml

Line in Ken should not continue until next step.
Same or similar topic here:
http://forum.plantuml.net/8024/lifelines-sequence-diagram-participant-repeatedly-destroyed?show=8024
and here:
http://forum.plantuml.net/7520/completely-remove-participant-sequence-diagram-after-been?show=7520
br,
Hannu