Thank you for your interest in Bizagi.
Concerning your question, indeed the attached signal events are not currently supported in the 9.1.9 version, and we have no current approximation (release or date) as to this feature’s release.
To cancel an activity, you may use a pattern in which the activity and an event are preceded by an Event Based Gateway. This will work as follows: once one of the elements (either the activity or event) is executed, then the others are no longer available.
To view more information and examples about the Event Based Gateway please review : http://wiki.bizagi.com/en/index.php?title=Event_Based_Gateway
Bizagi BPM Suite Support.