That's not exactly true, but we're talking spans on the order of years without power to start losing data.

Would a coin cell be sufficient to deal with the uncommitted writes still in the SSD's DRAM buffer?

In his The Amp Hour interview, the late Chuck Peddle described developing new DRAM-based SSDs where they were using super capacitors to power this flushing operation.

But I'd assume the coin cell in question here is a conventional RTC battery.

I hereby stand corrected!