DeeringAmps
John, your question has been answered;

 
It has, and to great satisfaction.  Thanks to all who responded.
JB

One power amplifier solid state circuit used during the seventies was called a cascade circuit.  The signal output of one transistor fed the input of the next transistor with each circuit transistor having an increasingly powerful output.  Unfortunately, a failure in one transistor would trigger a failure of all the transistors in the circuit.  It was easy to troubleshoot but expensive to repair.  The most common failure reason was no load connected.
 
So I agree with Tom, tube or solid state, why take the chance?

An Audio interface is really like a Audio mixer. 
It could sit there for ten years turned on with nothing connected and it would not really care. it will just sit there doing nothing minding it's own business. 
Even the headphone amp could be left cranked to max with nothing plugged in and it also doesn't care. 
I often walk away from my studio to go eat or ?  and all I do is turn off my power amp for my monitors as it's the biggest power suck,  it's a left over habit from doing sound. . My computer, mixer and interface stay turned on. Sometimes I never come back and forget I left it like this.. no big deal. 
 
Generally I just turn the volume right down while tracking with mikes. I can do this on the front of both my interfaces or the volume control of the power amp. I realize powered speakers always put this on the back. And that some interfaces neglected to have a monitor level on the front. That sucks and I would make sure not to buy an interface like that.