Please save me from an expensive mistake! Sonus Faber Amati Futura longevity concerns...

If you're truly "worried sick" you'd better listen to your gut, and make a decision you can be comfortable with. If you're "worried sick" before the purchase, that should tell you something that other folks' opinions won't assuage.

If you are "getting married" to these speakers, congratulations!

Please consider that you may be simply in the 'Honeymoon Phase', and upgrading speakers is usually a long-term partnership.  

I mention this because many of us focus on ONE item, in this case speakers, then later realize they desperately want new cables, or DAC, or Pre-Amp, etc. to make those speakers sing. 

If you can afford to improve your SYSTEM to accommodate the SQ improvement that the speakers provide, I say go-for-it. 

If on the other hand, you are a bit strapped after the honeymoon is over, you may have some long-term regrets because the money is gone and your speakers are not sounding their best.  

Just my 2 cents.

footnote:  from the 2012 review by John Atkinson...

"When I played the half-step–spaced toneburst track on Editor's Choice, the tonebursts spoke very cleanly down to this track's 32Hz limit. Repeating the track while I listened to the cabinet walls with a stethoscope revealed almost no spurious resonances other than a slightly live nature between 200 and 300Hz. The 1/3-octave warble-tone tracks on Editor's Choice sounded quite even from 300 to 63Hz, a little lower in level at 50 and 40Hz, and returned to full level at 32Hz, which is close to the lowest-frequency resonance in my room. The 25Hz warble tone was still audible, but the 20Hz tone was not. There was also no chuffing noise audible from the ports."

If low-end information is important to your, you may want to consider room treatments (now) and sub-woofers (someday) as well...

Is this a 1 owner speaker? Not sure what you mean "It's a buy back pair" Even if this is a mint one owner speaker don't expect 30+ years of trouble-free use. Unless you enjoy the DIY part of this hobby purchase new or dealer demo(warranty).

It’s true that speakers don’t last forever. But they do last a long time. That said, I wonder if you might consider a previous generation Homage series Amati or Serafino which followed the Futura. 

The Futura was a good speaker, though a bit warmer and more laid back than the Homage series. They go for about the same price on the used market as the Futura. And, being less “old”, they should go farther into the future for you. 

I actually auditioned a mint condition pair of Futura’s about 2 years ago, but listened to them vs. the current version of the Serafino. Though either speaker would be a fine choice, I’m happily listening to the latter in one of my systems as I type. Wonderful speakers.