Attending job talks when you are leaving the department
Impossible to answer well without knowing more and I don't think it is appropirate to post more on a public forum! 

I think it really depends on your relationships with your colleagues who you are leaving behind. In some situations it is better to absent yourself from situations where people are looking forward to the future of your old department. In other situations your experience may be helpful and it may be supportive to your colleagues who you will leave, but I guess who you want to stay on good terms with and continue to support. (I have not exactly been in this situation before, but similarish ones)