FastLed LED Strip Output Checksum
Look at timing on sheet 4 of the datasheet, and the times on sheet 3

A Low bit is 400 +/- 150nS wide Low followed by a 800 +/- 150nS wide High

A High bit is 850 +/- 150nS wide High follow by a 450nS wide Low.

To do what you suggest with a checksum, you'd have to send the checksum (minimum of 3 bytes to fake the data for an extra WS2812B for example) first, and see if the 24 bits were received correctly while at the same time the last 3 bytes were being sent out.

A Due might be fast enough to do that. I don't think a 16 MHz Arduino could.

Checking power level is not really feasible, as many strips get power attached to the beginning, middle, and end of a strip to ensure uniform brightness and to keep the strip's power traces from overheating from excess current flow.