How long should Pre amp (12au7) tubes last in Rogue Preamp?

I've pulled small signal tubes out of 70 year old radios / equipment that were still working. really depends on like others said how hard they are run also the quality of the tube.  IMO, NOS tubes tend to last much longer then their new counterparts but are usually much more expensive so its a trade off.  NOS tend to sound better but not always. New production tubes are getting better every year but also their prices have steadily risen. 

12AU7's are very common so you will never have issues finding them new or NOS so don't worry. 

Tubes are not exact as two identical units may be totally different.  Your ears and an occasional tube testing will let you know.  

Nos Mullards or telefunkens will last as long as you own your equipment. I’ve got some from the 50s and 60s that still test 90%. They must have at least 20 k hours on them. Obviously mine are not nos but I’d feel real comfortable paying good mo eye for them from Brent Jesse or another reputable tube seller. 

Gold Lions sound really good to my ears. They should last a good longtime in the Rogue

I haven't tried the Gold Lions yet, but I put a pair of NOS Tung-Sol tubes in the preamp section of my Rogue integrated amp and was surprised at how much better it sounded.  I'm sure my JJ's were still fine after a few years but it seemed like a cheap enough experiment and it paid off.