Is it being left to rot?
Hardly.
We were advised that the equipment will be progressively removed, to be used for spares. Towers, antennas etc. dismantled and sold for scrap. Buildings offered to landowners or dismantled for scrap.
Was disassembly & removal costs factored in to the economic case to retire these facilities?
No doubt, and if they were to be retained, the ongoing maintenance costs, cost of replacement/upgrade, ongoing land lease, electricity etc. etc.
NDBs & VORs were offered to the relevant AD owner/shire and flying club(s) to take over responsibility for, but few took up the offer.