You can't be a no-show for a flight BA have cancelled

You're not under a general obligation to accept their alternatives (they didn't work for you), so if don't accept, you can't no-show for that either.

Generally speaking, you are correct - you do need to fly on the flight to collect the TPs. You can't just book a ticket, not turn up on a flight that operates and expect BA credit you TP. Strange (or not) as it may seem, such a loophole would get used all the time by people who needed a few TP!

Where ORC comes into play, is if BA prevented you from flying on the booked flight because it didn't operate, and you needed to take an alternative routing. In that case, BA will award the TP because it was their fault that the flight didn't operate. As a personal example, BA cancelled a BRU-LHR flight about 12 hours before I was due to fly BRU-LHR-EDI earlier this year. Instead I flew directly BRU-EDI on Brussels Airlines. BA coughed up the 80TP (2 x 40TP legs) without any complaint.

So the suggested resolution in your case (and yes, I know hindsight is 20/20) would likely have been:

1) Decline the alternative on the basis the trip would have been in vain with the timings they offered you.
2) Don't cancel the ticket, as that ends BA's duty of care and obligations
3) Pay for your own alternative routing since BA could not provide one (they must be given a chance to, but you did that), claiming the cost back off BA after the event

In this scenario, you don't refund the ticket at all, you just pay what you were always going to pay, i.e. the cost of the ticket, albeit you would likely need to wait several weeks or more to get the refund for the train.