Right, quick background: bought second hand amp and speaker cab from ebay, seperate sellers. A Randall RM100 100w head and matching R212NXT 160w Cab.

All appears to be fine up until the first big band practice, after about two hours of very loud practice the amp goes silent. I check the back and two tube failure lights are on so I presume I've blown some tubes.

Get the amp repaired and on trying it out turns out that the speaker cab is dead, for the most part. I'm presuming something blew in the cab which left no load on the amp which then blew some power tubes.

I've taken the cab apart and can't find any loose wires anywhere, but even with a second amp the right speaker makes no sound and the left you can just hear a very quiet output, but sounds really distorted and rustly, barely tell it's a guitar at all.

So, how do I check if the speakers have blown? There's a possibility (although I'm sure I checked before hand) that the amp was set on 16Om and the Cab on 8Ohm. Could this put enough power out to destroy both speakers quite competely?

If so, is there parts that can be replaced or am i looking at a new speaker set? They're really nice custom neodymium Celestions...

Advice would be welcome. Thank you!
Check the impedance of the speakers. If they are dead - there is nothing you can do basically.
If you are sure there is no loose wires - the speaker is done. You can try and find someone to replace the voice coil for you if that was a really good speaker. If it ain't - it's time to upgrade.
You can get some Neodymium Jensens for replacement - they're damn good. And you can try and sell your blown speaker - someone who has the tools and gear might be interested in a good basket+magnet+diffusor.