BNB - how to manage holding it for binance fees.

Hi.
I've not been using BNB on Binance as I've been stumped by the maths involved in using it.

Using BNB gives you a 0.025% discount.
Say I bought 10 BNB to pay for my fees, then the BNB coin crashed by 50% but all other coins stayed stable.
Still using the BNB to pay for fees - would I now be getting a 0.0125% reduction in fees?
Or would I now have the equivalent to what was 5 BNB ... and using them for fees would be 'selling' them at a 49.9750% loss?

If it's the later.... how do you manage it?
I'd assume you'd have to take the role of a positional trader when buying the BNB. Even if your a day trader.
Would you keep stops on 90% of it? So you can utilise the rest for fees? Or seeing as you need it to use bots (i gather) Would you give it all to your bots?
Got me so confused..