This might be wrong, someone correct me if so... I'm thinking of the split that occurred as being nearly if not actually just like a stock or other securities s

This might be wrong, someone correct me if so... I'm thinking of the split that occurred as being nearly if not actually just like a stock or other securities split. In effect some portion of the original security 20% or so left. That reduced the market cap of the original security, and created a new market cap for the new one. Now it's possible the new one could eventually become worth 0 and the original would increase back to it's pre-split. A question this then raises for me, is if you went through this split, would you account for this in capital gains the same way you would with a stock split?