Definitely destroy the hard drive, smash it to bits, drill holes in it, whatever you can do. Deleting files, factory reset etc is not enough. There will still be traces of data there for a tech savvy criminal to find. Not worth the risk.
OK, so his bank accounts etc are closed, but you have no idea how much personal information may be on there - there could even be access to emails etc, with other people's personal info and so on. By leaving it, your father's personal identity could be stolen, which could then potentially facilitate criminal activity.