Yes, I often use my Yamaha 01v which is 44.1 only. I may return to a project that had used it later on and not have it turned on and the project loads and plays fine, it simply uses Sonars clock.  
So just use it and then move on. Your just stuck with 44.1 and that's been fine by me. My gear isn't good enough that anyone is going to know any difference. 
I'm not sure why your worried about sound fonts,, seems most left those behind in the distant past. We have much better sounds available now. 

RME has a super steady clock that doesn't create interruptions even when suddenly the master is lost - it'll just switch to its internal clock. You can leave Sonar's "timing master" to FF400 analog. The DSP inside the RME makes sure everything is synced to the S/PDIF input, it has nothing to do with Sonar. If you turn the Kemper off the RME should switch back to internal clock automatically.

Sanderxpander
RME has a super steady clock that doesn't create interruptions even when suddenly the master is lost - it'll just switch to its internal clock. You can leave Sonar's "timing master" to FF400 analog. The DSP inside the RME makes sure everything is synced to the S/PDIF input, it has nothing to do with Sonar. If you turn the Kemper off the RME should switch back to internal clock automatically.

Thanks for the insight Sander this is exactly what I was hoping.  That if the FF400 is slave to SPDIF and it looses the clock (i.e. Kemper powered off) the FF400 is smart enough to switch over to it's internal clock and assume Master.  It was then a case of how do I set Sonar.  I was guessing the best common denominator was "FF400 Analog" (over "FF400 SPDIF").  After reading more in the Sonar manual it seems the Sonar timer selections are geared more toward a Driver/Device than inputs.  In other words, it wouldn't matter whether Analog or SPDIF settings were chosen because they are both control by the same driver/device.  Assuming I read things correctly.  If that is true though it does raise the question of WHY then does Sonar have two separate FF400 selections - one for SPDIF and one for Analog?    Guess my only concern here is, when the Kemper is on and the FF400 is acting as SPDIF slave (and if Sonar is set to Analog) then will that cause Sonar to try and clock to the FF400 internal clock (which is NOT the master at that point)?  
 
Somebody on the RME forum explained to me that in my particular case I have no worries because the Master clock only comes into play with digitally connected devices (i.e. SPDIF).  So as long as I have only ONE digital device (the Kemper) ever during a session, then I won't have to worry about clock/sync/alignment issues between Sonar and the FF400.   Not sure if this is correct, but it was explained this way.

SonicExplorer

bitflipper
If recording via S/PDIF, you must select it as the recording timing master. 

...So if I were to turn it off, am I still okay to just continue on with Sonar still set to SPDIF as timing master?   

You only need to specify S/PDIF as the clock while recording from that source. Once you've recorded the track, you can switch back to letting SONAR do the clocking. In fact, you have to switch back once the S/PDIF source has been disconnected, since then the clock is no longer present.
 
As Sanderxpander notes, some audio interfaces are smart enough that it doesn't matter. That has not been the case with the interfaces that I've used (Roland, MOTU, Focusrite), but then I've never been in a position to afford an RME. 

bitflipper

SonicExplorer

bitflipper
If recording via S/PDIF, you must select it as the recording timing master. 

...So if I were to turn it off, am I still okay to just continue on with Sonar still set to SPDIF as timing master?   

You only need to specify S/PDIF as the clock while recording from that source. Once you've recorded the track, you can switch back to letting SONAR do the clocking. In fact, you have to switch back once the S/PDIF source has been disconnected, since then the clock is no longer present.
 
As Sanderxpander notes, some audio interfaces are smart enough that it doesn't matter. That has not been the case with the interfaces that I've used (Roland, MOTU, Focusrite), but then I've never been in a position to afford an RME. 

Hold on a moment bitflipper.... When you say I must have the master set to SPDIF when recording from that source, are you referring to the setting within Sonar as well as the FF400?   Because if you also mean the setting in Sonar, then that differs from prior advice of setting to "FF400 Analog" inside Sonar.

Yeh, I'm talking about the SONAR setting. I have never had to alter my interface's settings when switching between analog and digital. Bear in mind that I don't use a Fireface, so take anything I say with 64.79891 milligrams of sodium chloride.

Ok, reporting back.  Taking the advice & guidance from the forum, I went and performed a bunch of tests.  In fact, the FF400 (when set to Sync Mode) detects any changes in clock source and adjusts itself.  And choosing the "FF400 S/PDIF" setting in Sonar as the Timing master for Playback/Recording works well.  So, to sum up, when configured this way a person can track with the Kemper via S/PDIF, is free to turn the unit on or off at will, and keep working along in Sonar during the session.
 
Thank very much guys, appreciate the help!
 
Sonic

I'm quite confident setting S/PDIF or Analog as timing source in Sonar doesn't matter but it's already working well for you so yay!

EDIT: by the way, I would actually recommend you turn off the Kemper when you record anything analog with your FF400 because I would expect the RME clock to be much better.