Is it good to wire WS2813 LED strip DI and BI together?
This is based on a few sources including the (poor) datasheet.

My interpretation is that BIN should be connected to the previous LED's DIN. Then if the one LED fails, the next one will not receive any data on DIN, but it will receive data on BIN. It will switch to backup mode, where it uses the data from BIN, and ignores the data intended for the previous LED. This allows the rest of the chain to continue functioning with only one dead pixel, instead of letting the dead pixel break the chain completely. The chain will still be broken if two pixels next to each other are dead.