BA is not good at refunding money in the sort of circumstances you describe.

If you look through the EC261 thread in this forum you’ll see innumerable examples where BA will flatly deny refunds or compensation for what seem to be clear-cut cases - indeed, even with examples where they have previously lost at arbitration.

They rely on most people accepting their word, or not having the inclination to do the work on a submission to either the arbitration body CEDR or the small claims court process MCOL.

Of course, a subset of those denied do have the inclination, might well find their way here, and end up winning either in arbitration or court. Those are processes that cost BA far more in time, cost and effort to defend - yet I’m not aware of a single person that’s been blacklisted. From personal experience on one occasion, that includes me and the amount was a lot more than your friend’s upgrade would have been - and I’ve flown plenty of BA sectors since without issue.

In other words, BA accepts that if it’s obstructive then some people will decide to take matters further - S75 claims are just another one of those situations where they will shrug their shoulders and accept the consequences of that policy. Your friend has nothing to be concerned about - besides, right now BA really, really needs paying passengers!