I've just read a thread that was last replied on April 2019. I believe that need to be Moderated but it's almost dead. is it good to report such dead threads or simply ignore them?
It can depends upon case to case basis. Mostly there is nothing to report for the dead threads but if anything of the present is linked with something in the old thread, it can be of a value to report.
I would like to know which thread you are talking about here because there must be something in it which have made you to ask this question.