Hello Rodrigo,in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=838537#10 you are writing:
I am ready to adopt it [the dia package], I just need someone to sponsor me.
Are you still willing to adopt the package? I'd be ready to sponsor you.As a first step I'd suggest to send your patches upstream , so that they can be applied there.
Thanks & greetings, *t  https://wiki.gnome.org/Apps/Dia/HowToSubmitPatches